Upvote:12
Well maintained armor can last for a very long time. But within limits, due to normal wear and tear. I can't give you any particular length, but you can safely assume anything from 30 up to maybe 70 years. Why? Because recruits sometimes bought second hand armor from retiring evocati, of inherited it from their father if he had served in the legions.
The Lorica segmentata was retired in the late 3rd century. It gave good protection, but was maintenance intensive, and difficult to repair. (The copper parts reacted to the steel.)
By the end of the Roman empire lorica segmentata was already out of use for well over a century. The armor of the Romans was about the same as that of their opponents.
Upvote:34
Roman Empire did not fall suddenly. This was a slow process which lasted centuries. And there is no sharp edge between antiquity and dark ages. The period of decline was much longer than a normal service life of any arms. And there is no sharp distinction between the forces of the Empire and "Dark age forces". Many barbarians who destroyed the empire were formally serving the Empire.
EDIT. There are many good books describing this slow and complicated process in detail, beginning with Gibbons' classics which is still not too out of date. Of the modern books I can recommend
B. Ward-Perkins, The fall of Rome and the end of civilization,
Adrian Goldthworthy, Fall of the West. Slow death of the Roman superpower.
The Fall of the Roman Empire: A New History of Rome and the Barbarians by Peter Heather
The Roman empire started hiring barbarians long before its decline. Not only individuals but whole tribes were hired. The arrangements for settling barbarian tribes on its territory also began long before the final fall. In 212 AD Roman citizenship was extended to the whole population of the Empire. Gradually the sharp distinction between the Romans and barbarians disappeared.
Upvote:48
I would dispute your claim that Roman armour was superior. Roman armour mostly consisted of a mail shirt of varying length and quality, not dissimilar to that of the germanic tribes that overran the empire.
There were heavier, full-body suits, especially used by their cataphract cavalry, made from scale and lamellar, even covering the horses. However, that was very expensive to manufacture and maintain. And that was copied from similar armour used by a number of peoples further East.
You may be confused by the popular image of the lorica segmentata, made from bands of metal, that was used by the Romans from the 1st to the 3rd centuries. Its use ended before the end of the empire, and even throughout that period simple mail shirts were common.
Your reference to plate armour is also out of sync βΒ it was developed in the West from about the 13th century, well after the fall, and quickly became far superior to anything the Romans produced. Even the full-length mail suits it replaced provided better protection than the average legionnaire's armour.