Salve, guys!
Science (from the Latin scientia, 'knowledge') is:
1.- A system of acquiring knowledge based on the scientific method, as well as;
2.- The organized body of knowledge gained through such research.
Scientific method is a body of techniques for investigating phenomena and acquiring new knowledge, as well as for correcting and integrating previous knowledge. It is based on gathering observable, empirical and measurable evidence subject to specific principles of reasoning, the collection of data through observation and experimentation, and the formulation and testing of hypotheses.
(These definitions come from en.wikipedia.org).
These very basic definitions, mainly built with concepts from Newton and Popper, may be applied to some practices of the Classical Antiquity, like engineering (vg, SEE THIS PREVIOUS TOPIC).
They certainly cannot be applied to any therapeutics before the XVII Century and only to a handful of diagnostic procedures before that time.
Any Science is also practice. As any of today's branches of Science (vg, Physics or Biology), Medicine was only a practice before becoming a Science; after that, all ot them became (obviously) both practice and Science.
I think that in the history of knowledge, any step is the continuation of previous steps and the base for future steps: prehistoric, Ancient Near East, Greek/Roman, Arab/Medieval and so on.
The body of knowledge of Medicine (definition no, 2) is not an "invention" of anybody, the same way America wasn't an "invention" of Columbus (or Vikings, if you like). As with any Science, the knowledge is out there. You only have to find it.