How the Roman Army was Constructed
The army was grouped into a few levels. The first was the legion. A legion had 5000 men. Those were divided into cohorts of 500 men, so there were 10 cohorts in a legion. Then there is a century of 80-100 men. There are 5 centuries in a cohort, so 50 centuries in a legion. The century was commanded by a centurion. An aquilifer carried the sliver eagle in front of each legion.
There were also auxiliaries, which were less trained men, sometimes from a different region that Rome had conquered previously. They would run ahead of the legions and get the enemy in confusion, or they would march behind the legions and fire arrows into the enemy lines.
Each soldier carried a shield, one or two javelins, a sword, and a dagger. They wore plate or chain mail over a leather tunic, and either sandals or boots on their feet.
The Romans also had battering rams, siege towers, and catapults for demolishing structures in the way. They would use the battering rams to break down walls, while the siege towers allowed the soldiers to gain the top of the walls. The catapults would fire boulders into a wall that was in the path.
In conclusion, Rome had several strategies which made them so powerful. They had a good attack strategy, they were well armed and protected, and they had methods for demolishing enemy structures in the way.