I know this forum doesn't like throughout history questions, but I think I got it down to one specific subject.

Between the height of Greece/Rome and Medieval Europe, weaponry doesn't change much. You have bows (up until Welsh Long Bow 1346 AD?), catapults (Alexander the Great used Catapults to protect his military while they crossed a river at the Battle of Jaxartes! 329 BC), cavalry (Alexander had a horse he rode into battle), and impressive military tactics since Greece (arguably Troy, but I'm not sure). Yet, I would say the most impressive thing before gunpowder was the stirrup which won the battle of Hastings at 1066 AD (ref Connections by James Burke).

What was the holdup? My only guess is the Dark Ages due to the collapse of Roman civilization into Feudal society.