Guaporense

The history of Classical Civilization can be divided into two broad periods: the period in which it was rising and the period in which it was failing. From 800 BC to the time of Augustus, the civilization of the cities of the ancient Mediterranean was in the process of increasing sophistication of technology, economic development, demographic development, etc. From the time of Augustus to the 2nd century, it was apparently in a situation of relative peak and stagnation; then, from the mid-2nd century onwards, it started to collapse. This collapse occurred over all dimensions of society, and it even affected the production of artworks like busts. In Pompeii submerged by a volcanic eruption in 79 AD, during the economic peak of the ancient world, there are busts of common citizens of the town which were not even very rich but had their own busts, such as this banker:

There is no evidence that Huns ever were close to any of the Chinese kingdoms that existed at the time (in the 4th-5th centuries, there were many kingdoms in what today we call China:

My study is for the Early Roman Empire around 100 AD. Iberia was not heavily urbanized, considering it did not have many large cities compared to the size of the Iberian Peninsula. Archeological surveys suggest that Sicily had a comparable urban population to Iberia. I have used demographic estimates by Scheidel (2009) adjusted with other references (he appears to overestimate the population of Roman Iberia, considering the small urban population and other sources yield more conservative estimates for the Iberian population). Overall the Roman Empire had 65 million, excluding client states/provinces like Bosphorus, Armenia, Dacia, and Mesopotamia. Iberia was indeed huge, so its total population could not have been much smaller than around 5-6 million. Hence, its overall rate of urbanization was certainly pretty low compared to the rest of the Roman Empire. According to this framework, the city of Rome had 923,000 inhabitants, which can be thought of as slightly lower than typical estimate for Rome (about 1 to 1.2 million).For Pompeii, my estimate is 8,900 people, which is also slightly lower than the typical estimate around 11,000 to 12,000. Overall, according to these estimates, you had about 35 million people in the Western Half of the Roman Empire and 31 million in the Eastern Half. The urbanization rate was slightly higher in the Eastern Half, 17%, versus 15% in the Western Half. So perhaps the difference in development (as indicated by urbanization rates) between the two halves was not large enough to explain alone why the Eastern half of the Roman Empire lasted longer—the fact it was more defensible also important.

Been listening to a lot of Iron Maiden lately, one of their most underrated songs IMO:

I am actually working on a scientific paper regarding urbanization levels across the Roman Empire and Classical Greece. My methodology is based on archeological evidence. My conclusions so far: 1) The Classical Greek world was substantially more urbanized than any region of the Roman Empire (but the difference in rates of urbanization was smaller than estimated before, Roman Greece in particular was almost as urbanized as Classical Greece). 2) Roman Greece and Greek-speaking regions of Crete, Sicily, Cyrenaica, and the western part of Asia Minor were the most urbanized. 3) The ranking of urbanization rates by region is the following: 1. Mainland Greece, Sicily, Crete, and Cyrenaica (most urbanized) 2. Italy 3. Egypt (it was very urbanized, possibly be more urbanized than Italy) 4. Asia Minor and North Africa (roughly the same rate of urbanization in both regions, however Asian Minor population estimates include large rural populations in the interior of the region) 5. Syria 6. Gaul 7. Balkan provinces north of Greece, bordering the Danube 8. Iberia (surprisingly, it is mostly not urbanized although there were many cities in Baetica) 9. Britain (least urbanized) Rates of urbanization are estimated in terms of the proportion of the population living in cities with at least 5,000 inhabitants (smaller towns like Herculaneum and Priene do not count as urban by this method, but I had to use a high cutoff because archeological information regarding smaller towns is very incomplete). About 1/6 people in the Roman Empire lived in such larger towns and cities, with nearly 1/4 or 1/3 in the most urbanized regions and 1/20 in the least urbanized regions. This is a map of 885 surveyed Roman cities scaled by the estimated size of their geographical areas, which I used to make my estimates: Out of the 15 biggest cities among those cities with measured areas, 12 were Greek cities (often Hellenistic colonies), while 11 were in the Eastern Provinces and 4 were in the Western Provinces. In terms of East vs West, the rates of urbanization are not that different because Sicily, North Africa, and Italy were highly urbanized. While Gaul, Iberia, and Britain were not very urbanized.

The Eastern Roman Empire had the most urbanized and richest provinces. This was a product of the fact that most Classical Greek cities were in the Eastern Mediterranean; below is a map with the ca. 900 Ancient Greek city-states in which we know their geographical location (POLIS (stanford.edu)); notice how the regions populated by a large number of Greek cities closely matches the territory of the Byzantine Empire around the year 1000: While Romanization resulted in significant development in the Western half of the Roman Empire, it is still true that the Western half never reached the same degree of development as the Eastern half. Hence, when the Roman Empire was broken into two halves, the most developed half lasted a thousand years longer. I wouldn't think it is particularly due to Constantinople being hard to conquer, while it being a fortified bastion helped to deter critical attacks; it's also true that the Byzantines held over much more land than just Constantinople for most of the thousand years they outlasted the western empire. So, I think the East's survival was mainly due to a combination of being: (1) Having more developed lands that could pay more taxes, so they were capable of supporting more, better trained, and equipped soldiers. (2) These lands were in strategic positions that were more defensive (in particular, the city of Constantinople, but also the provinces of the Eastern Roman Empire had a smaller frontier with the northern European tribes. And the Sassanid Persians, despite their historical enmity with Rome, were a bit less dangerous than the Northern European tribes (in my evaluation).

If you take a look at that book can you give some background on the people they call scientists. Basically, it says that in modern times we have the development of modern science, in antiquity they did not develop modern science, but there were people who were doing work that today we would call science. The largest number of such people were active during the Late Republic and Early Imperial periods. In regards to technology, there was very substantial technological progress from the time of the Early Republic to the Early Empire. For example, in 300 BC there did not exist watermills (which were the biggest technological advance in energy technology until the Watt's steam engine in the late 18th-century), keyboard instruments, mechanical geared devices, nor domes, nor sophisticated concrete structures or arched structures. All these were invented over the next few centuries. As a result, the Pantheon build in the early 2nd century AD would be science fiction for people living at the time of the First Punic War. Other technologies invented during this period include the heavy plow (the Romans described it being used in the heavy soil of Roman Gaul and Germania) and the Gallic mechanical reaper. This old scientific american article from 1979 is a good description of how ancient catapult technology evolved: Ancient Catapults on JSTOR

They say that regarding the general situation of the ancient world as a whole rather than individual cities. In the case of Constantinople, it grew because the emperor moved the capital there, so it grew much larger, despite the overall decrease in urban population across the empire compared to the level a few centuries earlier.

Well, it's generally agreed by specialists that Classical civilization as a whole (that is, the civilization that was unified under the Roman Empire) started to decline (in economic, technological, and demographic terms) around 100-150 AD. With the economic decline and decline of long-distance trade, cities started to lose population as well, while people migrated to the countryside to live as self-sufficient farmers. This process took several centuries, and the end was the creation of the medieval world. Rome's population collapse was more dramatic than other cities because it was much bigger (partly thanks to subsidized foot and entertainment paid by the provinces), but it was just part of a general trend: the fact is that it continued to be the largest city in Western Europe until the rise of Cordoba in the 10th century.

Actually, there was a lot of scientific progress from 600 BC to around the of Augustus, then the number of scientists peaked in the first 150 years of the Roman Empire. After the early 2nd century AD, the number of documented scientists collapsed. This is documented in the number of recorded cases of ancient scientists from Keyser and Irby-Massie (2012), who recorded a timeline of about 2,000 ancient scientists (mostly Greek and Roman, but also some Persian and Jewish authors as well, see Amazon.com: Encyclopedia of Ancient Natural Scientists: The Greek Tradition and its Many Heirs: 9780415692632: Keyser, Paul T., Irby-Massie, Georgia L.: Libros): Technology also made substantial progress in Classical Antiquity. For example, buildings like the Pantheon would be inconceivable a few centuries earlier (and also became impossible to build after the fall of Rome until relatively modern times). Then, scientific and technological progress stopped during the period of the greatest power of the Roman Empire due exactly to the centralization of power in the emperor. Alain Bresson (2016) indeed blames the centralization of power into the Roman Empire for killing the institutional foundations of Classical society, which was the autonomous city-state. Ancient science and technology progressed a lot during the Archaic, Classical, and Hellenistic periods, the age of city-states, and even during the beginning of Roman hegemony, cities around the Mediterranean world continued to function as city-states, operating independently of Rome except that they didn't start wars with each other (unlike the Classical period), so scientific and technological progress continued, peaking around the time of Augustus. It was the gradual centralization of power in Rome, starting with the Social War in the early 1st century BC, which incorporated all of peninsular Italy into Rome, and finishing with the centralized bureaucratic empire of Late Antiquity, that killed independent thinking and, therefore, hindered further scientific and technological progress. After the prosperity of the Early Imperial period (which economic historian Peter Temin states, Early Imperial Rome was likely the most prosperous society that existed before the Industrial Revolution), it took about 500-600 years of slow but dramatic economic and demographic decline for the Roman Empire to lose most of its territories, becoming the tiny Byzantine state of the early 8th century. By then, however, cities across the Mediterranean were mostly abandoned, long-distance trade in bulk commodities disappeared, and there were no economic resources available to support scientists in advancing the knowledge accumulated by the ancients. Then it took about a thousand years for the European population densities to surpass the Roman peak, and with economic recovery, particularly in the city-states of Italy and the Hanseatic League to the north, the Renaissance blossomed. Still, in the 17th century, the famous mathematician Leibnitz cited Apollonius of Perga from about 200 BC as an example of cutting-edge mathematics. Thus, it was only in recent centuries that modern western civilization fully surpassed the ancients.

I recommend Mogens Herman Hansen's work, in particular, his work on the Athenian Democracy and on the Classical Greek City state: Amazon.com: Polis: An Introduction to the Ancient Greek City-State: 9780199208500: Hansen, Mogens Herman: Libros Which made me think that city-state societies tend to be more modern and dynamic than traditional societies of territorial states. In Medieval Northern Italy, there emerged a society of 300 city-states, of which cities like Florence and Venice were the largest. Connected to the mediterranean sea, these city-states traded a lot and achieved a very high level of economic prosperity so that by the 14-15th centuries, Northern Italy was (likely) the richest region on the planet. When people achieve a relatively high level of economic development, they have more free time to think about ideas and to work in art. That is why artistic flowering are strongly correlated with periods of economic prosperity (such as the artistic flowering in Late Classical, Hellenistic, and Early Imperial Roman art, Renaissance Italy, and Golden Age Netherlands).

The Roman Empire was formed as a thalassocratic empire: it was basically formed as a network of city-states around the mediterranean sea under the hegemony of the city-state of Rome. This empire expanded towards the northwest of Europe, as this region was very close to the Mediterranean region with direct access from the region of Gallia transalpina, where Julius Caesar based his invasion of Gaul. Most Roman wars were not wars of conquest but instead wars for the security and hegemony of Rome. As noted by many authors, the empire of Rome was formed slowly in these defensive wars. Even Caesar's conquest of Gaul was defensive: he responded to the request for the defense of the southern gallic tribes around the region of Gallia Narbonensis (already a Roman province). Trajan's invasion of Parthia was something very different. Not a defensive war; it was an attempt at invading the Parthian Empire, which was a Central Asian empire controlled by semi-nomadic horse archers. One should note that most of the border between Roman and Parthian territories was desertic, except for some small inhabitable areas around the Tigris river. Thus, it did not make any sense to annex territories there. This invasion also had no defensive purpose, as Syria was not under Parthian military threat for over a century: Trajan invaded it for the glory of doing so. Once he died, Hadrian took office, and he quickly abandoned Trajan's conquests. I should also note that Trajan's Parthian campaign is not well documented in our sources.

As I already stated in another post, the time around 1 AD was a period of peak economic prosperity for the Mediterranean world and so they imported large quantities of exotic goods from faraway places. The Classical civilizations of Greece and Rome had more awareness of the existence of India than of China (which was geographically separated from the rest of Eurasia by the Himalayan Mountain range), as Alexander the Great himself had conquered a substantial portion of the Indian subcontinent.

Among historians specialized in the subject, there are two views: the small Rome view, which states that Rome had about 500,000 to 600,000 inhabitants, and the big Rome view, which states it had around 1 million people or even more. The small Rome view comes from the fact that Imperial Rome had a walled area of 1,373 hectares which is enough for 500,000 people at twice the density estimated for Pompeii (the city of Pompeii had walls enclosing 66 hectares and a population of around 11,000-12,000). However, excavations in Ostia, Rome's port city, show that densities much higher than Pompeii were possible, apartment buildings typically had 3-4 floors in there, in Rome proper they were even bigger (bigger cities means taller apartment buildings because land becomes more valuable, Augustus regulated building codes stating heigh limits for insulae at 70 Roman feet, enough for 6-7 floors): In addition, we know that Augustus' division of Rome into 14 regions covered a substantially larger area than the Aurelian walls (built in the late 3rd century, when the city of Rome had declined in population from its peak during the time of the Late Republic and Early Empire). Based on the archeological evidence and Augustus', Hanson and Ortman's (2017) model estimates that Rome had 923,000 inhabitants, very close to the 1 million figure typically estimated. (PDF) A systematic method for estimating the populations of Greek and Roman settlements (researchgate.net) We should also consider that Rome had substantial suburban neighborhoods, as well as ancient writers describe the lack of clear distinction between the city and the countryside, stating that Rome looked like it could stretch forever. The ca. 900,000 figure might be accurate for the city center. Still, there were hundreds of thousands of people living in the suburbs, so Rome's ancient metro area might have approached something like 1.5 million around the 1st century. Thus, the city of Rome's likely population history in antiquity was: 500 BC: 15,000 (about 30,000 in the city-state, according to Walther Scheidel's estimate in his 2019 book) 300 BC: 90,000 (from Beard (2016), 1 million citizens in the whole city-state) 225 BC: 150,000 (from Keith Hopkins) 30 BC: 900,000 (big jump in growth following the Punic Wars and the conquest of the ancient mediterranean, Rome surpassed Alexandria to be the largest city in the Ancient World, Keith Hopkins estimate Rome approached 1 million people by the time of Augustus) 50 AD: 1,200,000 (perhaps the peak was reached around this time, when they had to build new aqueducts, so population probably increased from Early Augustan period) 275 AD: 600,000 (empire was already in economic and demographic decline during the crisis of the 3rd century, by this time most of the city was enclosed in the 1,373 hectares of the Aurelian walls). 800 AD: 25,000 (population collapse following the fall of the Western Roman Empire, Rome still remained the largest city in Western Europe, with about 20,000 to 30,000 inhabitants, as urban populations collapsed all over Western Eurasia).

The period of the Late Republic and Early Roman Empire, around the year 1 AD, represented a historical peak in economic prosperity for the Mediterranean world, and when people had extra money available, they consumed luxury goods. Importing exotic goods from distant places like India was a consequence of this prosperity. Consumption of goods from India was not exclusive to the elites: Roman soldiers in Britain consumed Indian pepper. Although it is true that trade with India was mainly restricted to high-value goods like pepper and not bulk commodities like wheat or bricks. Inside the Mediterranean, the physical scale of trade was much greater, as African bricks have been found on Roman buildings in Italy.

I would have been very interesting if the Roman Empire had breakup into several smaller states. It might have become like early modern Europe: several large but similarly sized states.

Ancient agricultural productivity A few decades ago it was typical to assume that ancient societies were all subsistence farming societies where agricultural productivity was very low, just enough for the bare survival of the average ancient peasant farming family with perhaps a small surplus to support the assumed 10% or so the of the population that was not engaged in food production. However, as historians in recent decades have applied the insights of modern sciences into ancient societies, as well as the insights from modern studies of other better documented pre-industrial economies (British Economic Growth 1270-1870 (2015) remains the gold-standard in the analysis of pre-modern economic growth) we have been able to properly appreciate how varied productivity levels could be in the pre-modern world. For example, according to British Economic Growth, agriculture corresponded to only 45-50% of the GDP of England during the 14th to the early 17th centuries, which shows that manufacturing and services were already half of the economy even in England during the late-middle ages. England was not a very exceptional pre-modern economy before the 17-18th centuries, in fact, its estimated rate of urbanization was around the European average in the 16th century (roughly ca. 9% of the population living in towns over 5,000 inhabitants in both cases), which suggests that it was not an economy with an exceptionally small farming sector. Therefore, we can infer that it was not atypical for pre-modern farming to be productive enough to support a large population that was not directly engaged in agriculture. In regards to ancient and medieval agricultural productivity overall, it is likely that the traditional model of mostly self-sufficient peasant households characterized farming in most ancient and medieval societies. However, there were many exceptions. For example, the evidence currently suggests that the agricultural system of the Early Roman Empire was likely very different. In its most developed regions such as Italy, farming was dominated by highly efficient large farms that functioned as business enterprises and exploited economies of scale and regional specialization, allowing for much higher levels of productivity than typical of subsistence farming. One example is the implied levels of Roman farming productivity that can be inferred from the agricultural manuals of Varro, Columella, and Cato. Columella writing in the 1st century AD, during the zenith of classical antiquity, wrote the following table of labor days required to farmland: We can conclude that in those well-managed, almost industrial farming states a farm laborer by working 300 days per year could cultivate 50 iugera of barley fields (which was the cheapest ancient stable grain), using 250 modii of seed or 28 iugera of wheat fields. To determine how much grain they could produce based on yield level, as ancient sources state, according to Goodchild (2007): “The scant ancient references we have for ancient yields in this area range from Columella’s cereal yield of 4:1 for the whole of Italy (Rust. 3.3.4) to the exceptional yields of 100:1 for Sybaris mentioned by Varro (Rust. 1.44.1) and Pliny the Elder (NH 18.94-5). For Etruria, an area noted for its fertility, Varro (Rust. 1.44.1) gave maximum yields of 10-15:1. The remaining passage is from Cicero (Verr. 2.3.112) where he claimed a yield of between 8-10:1 in the land surrounding Leontini in Sicily.” (Goodchild page 247) Based on a combination of modern data with ancient sources, Goodchild (2007) estimates that median crop-yield in Roman Italy was perhaps 6.5 to 1 to the quantity of seeds sown: This means that a Roman Italian farm laborer could perhaps produce 1,625 modii of barley per year, which is about 14,000 liters of grain, or 11 metric tons of grain. In terms of wheat, it took about ¾ more time to work on the same land, which a similar yield, which means a Roman Italian farm laborer could work on 28 iugera of land working 300 days per year, seeding 140 modii of wheat and producing about 910 modii of wheat, or about 8,000 liters of wheat per year. This explains why the rich in antiquity ate wheat bread while the poor and slaves ate barley bread. At a productivity level of 14,000 liters of grain per year, it is possible for a single Roman Italian farm worker to produce enough barley to feed 35 people (given each individual needs about 2,000 to 2,500 calories per day which can be supplied with 400 liters of barley per year) or enough wheat to feed 27 people (as the density of calories in wheat is larger so only 300 liters are required per person per year, thus the difference in calorific output from shifting from barley to wheat is smaller than in terms of liters, still barley appeared to be 20% cheaper than wheat in terms of the cost of calories). Other grains like beans and millet appear to have had labor input costs between wheat and barley. At the median yield of 6.5 per seed, Columella’s farm of 200 iugera crewed by a workforce of 8 workers plus two pairs of oxen would be expected to produce 6,600 modii of grain in total, roughly 60,000 liters of wheat. If producing at the high fertility region of Etruria with yields around 10 to 15, according to Varro’s account from the late 1st century BC, such a farm with 8 workers could reach an output of 50 to 75 modii per iugerum or 87,200 to 131,000 liters of wheat. One has the impression that Early Imperial Roman farms were highly productive grain factories manned by slaves rather than self-sufficient peasant farms. In fact, given estimated wheat consumption of 160 kg per person (excluding calories from other sources such as meat, wine, and olives), the population of ca. 65 million inhabitants for the Roman Empire in the 1st century could be fed with only 120,000 of such high-performance Etrurian-wheat farms employing only ca. 1 million workers. These productivity levels are the Roman Italian ideal for the 1st century: we are assuming that the land was optimally managed, that it was good fertile land without many rocks or trees (which as Columella stated, to deal with trees would require 3 additional laborers to cultivate 200 iugera of land), and these estimates only take into account the labor cost of producing the grain, without considering the costs of processing the grain, transporting it to retail markets, and selling it. Thus, retail prices of grain suggest a Roman Legionary soldier in the late 1st century, who made 1,200 sesterces per year, could purchase about 400 to 600 modii of wheat (as provincial wheat prices varied from 2 to 3 sesterces per modii), roughly half of what a laborer could produce. Thus, we cannot make inferences about typical ancient income levels in terms of grain from these ancient agricultural manuals. While this represents the upper bound in estimated productivity, the current evidence suggests that it is likely that only a small minority of the Roman workforce was directly employed in the production of grains. Roman Italy in particular was a net importer of grains, as land was relatively expensive in Italy compared to the more peripheric provinces, so it was better to use the premium valued Italian land to produce more expensive foods such as wine and olive oil, as land yields in wine and olive oil were substantially higher (I read some estimates that it was possible to produce 4 times the calories in terms of wine compared to grain on the same amount of land). In farms in Roman Gaul, where land was comparatively abundant given the much lower population density, the Romans focused on maximizing labor productivity to an even greater extend: they even developed the first documented case of reaping machines, besides Roman Vallus, reaping machines would only reappear again in modern times. Thus labor productivity in Gallo Roman farms was probably even higher than the ideal levels of productivity deduced from the Roman writings about Italian agriculture: Roman Egypt was understood to attain higher levels of comparatie productivity for grain versus other agricultural goods such as meat, olive oil and wine. This is why it was the Empire’s major wheat expoting province, however, it could be the case its productivity levels were lower than Italian levels, but the difference was smaller in grains than in other agricultural goods, explanining the relative specialization of Italian farms in non-grain crops. I do not have access to any documents that allow us to estimate labor productivity levels for Roman Egypt, although in terms of wheat yields relative to cultivated land they appear to have been higher than in Italy (which were perhaps around 30-35 modii per iugerum). Agricultural labor productivity in antiquity could be much lower than 8-14 thousand liters per worker per year. This should be understood as to be near the maximum attainable output per worker at the zenith of the Classical Civilization during the Early Imperial Period (30 BC to 180 AD), a place and time as Peter Temin has conjectured, humanity reached its highest living standards attained before the Industrial Revolution. In other ancient societies labor productivity levels in agriculture were likely lower. For example, in the labor-abundant and land-scarce Ancient and Medieval China, as Von Glahn (2016) states, farming was done by small and mostly self sufficient family farms, it was thought to be typical for a family farm of 5 people (usually 2 adults and 3 minors) to produce only 3,000 liters of grain per year: This implies an output of roughly 600 liters per person of the household or roughly 15 to 25 lower than the output per worker of an 1st-century laborer in Columella’s farm producing wheat or barley. However, as the family was self-sufficient they had to process the grain as besides cultivating it and naturally, labor productivity of the women and children who helped in the farm would be naturally lower than that of an adult male (which I guess is what Columella calls a laborer). Productivity levels around 600 liters per person in Chinese peasant families are consistent with estimates of Chinese economic historians of Han-period productivity levels of about 1,000 jin of grain per unit of the agricultural population, which translates to 640 liters, roughly 1.6 to 2 times minimum subsistence. These lower productivity levels are consistent with the concept that historians often imagine of the small self-sufficient farming households that sell a small proportion of their output to the market and consume most of their output for their own subsistence. In Classical Antiquity, these small and low productivity family farms were common as well during certain places and times. For instance, in Italy the Early Republic, but as Italy became more developed and integrated into the “Mediterranean economic zone” during the peak of economic activity in the Late Republic and Early Empire small farms were displaced by larger and more efficient latifundia. Indeed, Columela’s highly efficient farm with 200 iugera of farming land, or Cato’s wine orchard of 240 iugera appears to have been around the typical Early-Imperial Italian farm size (from Goodschild (2007)): For comparison, typical ancient and medieval Chinese family farms had around 40 to 100 mu (Von Glahn (2016), the 2 AD census measured 827 million mu of cultivated lands, or about 70 mu per rural household given China had ca. 60 million inhabitants or 12 million of their typical 5-person households, of which about 11-11.5 million were rural households ), each mu was 457 square meters, an iugerun was 2,523 square meters, which means typical Ancient Chinese peasant farms would be around 7 to 18 iugera, roughly 3.5% to 9% of the median Early Imperial Roman Italian farm size. However, yields per unit of land and seed were likely higher in Chinese farms, as they had lots of people and little land, they had to focus their efforts on maximizing the yield of their small farms. This is why they developed technologies to not waste precious seeds like the seed drill, while Romans invented technologies to maximize labor productivity like the gallic reaper. It was perhaps an analogous dynamic to the late 19th century USA and Germany: the USA had lots of lands so they developed farming machinery to use that land, Germany had little land, so they focused efforts to develop chemical fertilizers to maximize yield per unit of land.

Serious historians specialized in Roman history estimate that Rome had around 1 million inhabitants. This estimate is based on two facts: 1. Augustus claimed that 300,000 to 200,000 Roman citizens received free grain, given adult males were 28% of the population in ancient societies this implies that Rome's citizen population was close to 1 million, adding slaves and metics and you get to over 1 million. 2. The area enclosed by the 14-regions of Rome delimited by Augustus was1783 hectares, a statistical analysis on the number of apartments that archeologists have identified in Roman cities suggest that Rome's population density might have been around 500 to 550 per hectare, which yields a population around 900,000 to 1,000,000 for the Rome of Augustus. See Hanson and Ortman (2017): https://www.researchgate.net/publication/321077578_A_systematic_method_for_estimating_the_populations_of_Greek_and_Roman_settlements So, the density of Rome appears to be 50,000 inhabitants per hectare, about twice of Manhattan. Manhattan's density is not that high compared to the density of some agglomerations in developing countries. The favela Rocinha in Rio de Janeiro has 100,000 inhabitants in 140 hectares, roughly 3 times the density of Manhattan: Ancient Rome's insulae were perhaps not very different in terms of density, this is a professional reconstruction by the Madrid's museum:

This is a graph on the shipwreck data with the lead pollution data, the two are very strongly correlated. The lead pollution data was extracted from a lake in Italy. Levels of lead pollution indicate levels of lead production as ancient smelting resulted in the emission of a part of lead production. Lead was a by-product of silver production and therefore indicate levels of silver production. Since silver was the standards money of the time, silver supply reflects the overall demand for money and hence reflects the level of commercial activity: source: Ian Morris, Social Development, page 46, on IanMorris.com. Also I have gathered the shipwreck data broken by 20 year periods instead of 100 year periods: from Quantifying the Roman Economy, page 221 Shows a bit greater resolution.

That's true. Not all knowledge is based on formal education. It is not correct to classify all workers without formal education as unskilled laborers. Ancient Roman cities were much bigger than mediterranean cities of the 12-13th centuries. The largest mediterranean cities of the middle ages had 100,000 inhabitants, Venice and Genoa, while in the first century Rome had 1 million, Alexandria, Antioch and Cartage each had around a half a million. The 5 largest cities in the Roman Empire in 100 CE had around the same aggregate size as the 4-5 largest cities in the world in 1700 CE. According to this site: http://www.tulane.edu/~august/H303/handouts/Population.htm The populations of the largest cities in the early Roman Empire were these: Rome - 1,000,000 Alexandria - 500,000-750,000 Carthage - 350,000-500,000 Antioch - 350,000-500,000 Ephesus - 350,000-500,000 total: 2,550,000-3,250,000 average: 2,900,000 While according to Chandler's "4000 years of urban growth", the population of the largest cities in the world in 1700 CE were: Istanbul - 700,000 Edo - 688,000 Beijing - 650,000 London - 550,000 Paris - 530,000 total: 3,118,000 Keith Hopkins said that in his article on the political economy of the roman empire, that the cost of transport by sea was 50-60 times cheaper than by land during ancient times. So these huge cities had to be feed on grain carried by sea, since transporting the food by land over hundreds of miles would be unfeasible. Huge merchant fleets kept those cities alive. Literary accounts said that some merchant ships carried over 100,000 amphorae, that would mean ships of 4-5 thousand tons of more. Larger than many merchant ships of the early 19th century. It would be only natural that commercial activity in the mediterranean would be 10 times greater than during the middle ages. The size of the urban economy (i.e. the economy that doesn't depend only on subsistence production, but also production for the market) in the Roman empire was very large if compared to other pre-industrial societies.

Are you sure about that? I would think that if anybody had superior weapons and armour would be the Hellenistic powers of the eastern mediterranean or Carthage. That depends on the enemies. Carthage, Macedonia, Ptolemaic Egypt, the Seleucid Empire and other mediterranean powers had comparable technology, social and economic development to the Roman Republic. One has to understand that economic, social and technological factors determine to a great extent the military capabilities of a State. These enemies were Rome's equals because they shared the same civilization with Rome: the classic mediterranean civilization. By the 1st century, the Parthians and the barbarians tribes were far inferior to Rome in terms of military strength, on all levels. Carthage and Rome fought each other in the 3rd century BCE, when Rome's armed forces were still developing. Sassanid Persia started in the 3dr century CE, when the Empire was weaker than during it's peak. Neither nation fought Rome at their peak. Because they won. The Romans managed to defeat every enemy that stood in their way from the 8th century BCE to the 2nd century. That's nearly 1 thousand years of military glory. By the early empire nothing could compare to Rome in military power. They considered that anything outside the empire wasn't worth conquering.

The most impressive fact about ancient Rome was the process of rise and decline of ancient civilization. By the 1st century CE ancient roman civilization had reached a degree of social, economic and technological development much greater than anything ever before and, perhaps, anything after for 1500 years. One interesting thing is the continuous process of decline that lasted for centuries, declining from the first century peak to the eight century and then recovering from the 8th century onwards. This can be illustrated in this graph on the levels of lead production of the world, that we can calculate based on archaeological data on dated ice cores from Greenland: source: "Greeland Ice Evidence of Hemispheric Lead Pollution Two Millennia Ago by Greek and Roman Civilizations", Science, vol. 265, n. 5180, pages 1841-1843. According to these estimates the world lead production started around 3,000 BCE and increased more or less continuously until the first century CE, when it was nearly 100,000 tons annually, then decreasing to less than 5 thousand tons annually in the early middle ages and increasing again to over 100,000 tons annually at the beginning of the industrial revolution. This type of evidence is also supported by various others archaeological findings, like shipwrecks in the mediterranean. It it something unique in human history, that otherwise shows a continuous process of improvement in social, economic and technological development. The Roman case is a case where people in the 11th century can look back a thousand years and really say that there were much greater empires and that the world today is only a shadow of it's past. That is something fascinating.

The east was much richer than the west during the 1st centuries BCE and CE. However, Italy and the western provinces increased in wealth during the early empire, at least according to the archaeological evidence, while the east stagnated or decreased in wealth after the 1st century BCE. This graph presents the chronological distribution of archaeological findings on Roman fish salting factories on Gaul, Spain Portugal and Morocco: source: http://oxrep.classics.ox.ac.uk/nw/index.php?option=com_content&view=article&id=40%3Aquantification-of-fish-salting-infrastructure-capacity-in-the-roman-world&catid=13%3Aproject-generated-research&Itemid=163&showall=1 The economic expansion in the early roman period for the western provinces was great. While in the 1st century BCE the east concentrated the bulk of the tax revenues, with time the west gained importance. The difference between the east and the west by the 2nd and 3rd centuries CE was much smaller. For example, out of the 5 largest cities in the empire, 2 were in the west, Rome and Carthage, while 3 were in the East, Alexandria, Antioch and Ephesus. We cannot say that the move of the capital to Constantinople in the 4th century had anything to do with the fact that the east was richer, as the hypothesis that the east was richer is quite in doubt for the 4th century.

The population of Roman Italy fluctuated greatly in history. Some historians, like Keith Hopkins, calculate that Italy in 250 BCE had about 4 million inhabitants, this population increased gradually, and by the time of Augustus, Italy may have grown to 7-8 million. According to some estimates Italy, made by Los Cascio, the population of Italy in the first century CE reached 12-14 million people (link: http://bmcr.brynmawr.edu/2010/2010-04-28.html). After the 2nd century the population of Roman Italy started to decline. Probably there wasn't a period of quick decline, with the exception of the plagues, but even in the case of plagues the population declined and them recovered (perhaps only partially after 2nd century). By the 6th century the population of Italy declined to, probably, ~3 million. This decline was the product of the decline in commercial and industrial activity, that forced the population of the Empire to work exclusively on agriculture, while Italy, a densely populated part of the Empire, lost it's ability to sustain a large population without it's commercial and industrial role, therefore the population migrated to the large provinces, like Gaul. Also, the decline in agricultural productivity and the overall economic decline contributed to increase mortality rates, which decreased population until it reached a new and lower equilibrium value.

I think that Rome declined gradually in size, while there wasn't any abrupt collapse in the city's population, with the possible exception in the 6th century. However by 500 CE Rome probably was less than a tenth of the city of 400 years before. Also, since the decline of Rome lasted for many centuries, there weren't many buildings standing in the mid 6th century as there were 500 years before. Only the ones made of marble and stone, like the Colosseum, that remained in mostly conserved state.