Reading Plutarch's account of the battle of Carrhae in 53 BC when Crassus led his legions into a trap, is like watching a slow train wreck. Aside from bad military decisions, he followed the advice of a local Arab who was obviously working for the Parthian king. This pattern of an elder political general who falls under the spell of an enemy agent was repeated in 9 AD when Publius Quinctilius Varus, aged 55, marched his 3 legions into an obvious German barbarian trap in the Teutoburg Forest. A later imperial power saw a similar calamity when British troops in Kabal, Afghanistan were ordered to retreat by their 60 year old General Elphinstone, who kept believing the promise of safe conduct made by the Afgan leader, resulting in the massacre of his troops in 1842.
The Romans suffered some other horrendous defeats, losing 50,000 to 75,000 men at Cannae in 216 BC against Hannibal, when they adhered to their crazy policy of alternating army commanders each day. Earlier, in the First Punic War against Carthage, the Romans lost their entire newly built fleet and perhaps 90,000 men in a great storm in the Mediterranean Sea about 255 BC. It is thought that the Roman vessels were top heavy due to the additional structure of a corvus or boarding bridge, thus making the ships unstable in heavy seas. But they just chopped down more trees and built another 140 ships and continued the fight.
Many people think of the Roman Empire coming to an end with the fall of Rome in 476 AD but they forget the Empire had been partitioned into western and eastern territories, and the eastern part, becoming known as the Byzantine Empire, lasted almost another thousand years, falling to the Ottoman Turks in 1453. This event precipitated the influx of scholars with their classical Roman and Greek texts to Italy and the West, giving a further stimulus to the nascent Renaissance which was to fundamentally transform and energize western Europe.