Amazing. At its best, the Roman world provided a vast area in which it was safe to trade and to move about. This did not occur again until the height of the European empires in the 19th Century — conceived of and administered by men educated to revere Rome’s accomplishments.
Gunpowder was one of the keys — when the Turks came charging in and became an early customer for cannons, it allowed them to blow holes in the famous walls of Constantinople in the 15th century. The earliest recorded use of gunpowder to take a city was from China in the 12th century; mostly the adoption of gunpowder in weapons among the hidebound muzzie leaders was pretty slow (now they pretty much use it on everyone and everything, every day); in Europe it was already of interest in the 14th century, and used against the muzzie occupation of Iberia during the Reconquista; the presence of cannons led to the decline of curtain walls and in some extreme cases to the redesign and remodeling of entire towns in Europe; by the early 16th century European countries (including now-vanished and subsumed principalities and city-states) with navies had altered ship designs to accommodate the bronze cannon then in use; in England Henry VIII got a bug up his tail about the low reliability and short useful life of the bronze cannon on his ships, and recruited from various German states the coal miners and iron metallurgists that would allow for iron-based cannon on land and sea, and after some mishaps (like the Mary Rose capsizing) led to another redesign of naval vessels, Hank became the father of the modern British navy, and the late start at overseas colonization really took hold in Britain.
Superior firepower remains the reason there’s any persistent civilization on the Earth today. And sorry, any snowflakes tuning in late, I’m not sorry for pointing that out.
https://en.wikipedia.org/wiki/Gunpowder_artillery_in_the_Middle_Ages
Romans in China, some posts:
http://www.freerepublic.com/focus/news/1814182/posts?page=9#9
http://www.freerepublic.com/focus/news/1814182/posts?page=28#28
http://www.freerepublic.com/focus/news/1814182/posts?page=34#34
Oh, I replied to the end, first, and didn't get back to my original idea -- the Roman Empire failed for a number of reasons, mostly political, but one of the other reasons is, they no longer had a military advantage, and didn't adapt or co-opt new technology.