Before I state my opinion, by mentioning who the greatest roman was, you need to think about how the romans felt about this. Bloodline was very important to Rome, they would not just call anybody romans, even though the citizenship of most of Italia, as well as their various provinces. To ask your self who the greatest Roman was I think you need to think of who on your list was a true roman and who was not. The likes of Gaius Marius and Pompeius were both great generals and leaders, but they would never be considered romans, because of their Italian blood. Marius was from Arpium and Pompeius from Picentine. They were able to gain such high ranking because, marius married a Julian, the family with the highest blood, and Pompey's father was a general for rome as well as a senator. Pompeius also married a Julian, Caesars only daughter, with a roman wife, Julia. So to correctly reply to this question, since Caesar has been eliminated from possiblility, since he was by far the greatest roman, I would go with his great nephew, and adopted son, Octavius "Augustus" Caesar. Octavius was the first declared emperor, even though caesar was made dictator of rome, until that fateful day on the Ides of March, 15, 44 BCE. Augustus started the empire with a great start as he was the start of Pax Romano age, the golden age of rome, relative peace throughout the empire for almost 200 years I believe it was, until the last emperor Marcus Auerilius, not the gladiator one, died and his son Comodus took the ivory chair and ended that era, so my choice if caesar is unavailable is Octavius August Caesar.