Why were the Roman armies so unbeatable?
They were not unbeatable: Hannibal proved that. But they were very good at doing what they did in general. As in many other times they use others to do the actual fighting for them, and then claim the glory as their own. But generally they are well trained and cohesive, even in defeat at Cannae they breach Hannibals defences line, though at great cost. Again as a generalisation their leadership is good, Julius Caesar & Scipio Africanus being pre eminent. They show the value of Imperialism, they make themselves look unchallengable because they establish a reputation for high military standards. But they were ultimately defeated, though the Roman Empire lasted for a very long time, hundreds of years.
