The Romans technology was the first point to answer this question. The ‘scorpions’ fired iron tip bolts, used in the first stages of attack and during the sieges. It fires arrows at incredible speed so it can pierce armor, and kill instantly. Although an effective anti-personnel weapon, the ‘scorpion’ is of little use when building and attacking. For that, Romans need something that can be approached with a heavier attack like the onager and the ballista. These piece of technology fires large stones at the enemy. They propel projectiles so high into the air that they can break down enemy walls, which meant that they could enter enemy’s territory easily. This is one of the reasons that the Roman army was so successful.
The next reason why the Roman army was so successful in battle was because of their legionary equipment like the shield, which was used not only for defense but also attack, the gladiolus, which was for stabbing other than slashing. Stabbing was more effective than slashing because it would severely injure or instantly kill unlike slashing, which would just wound the opponent. The sword was narrow, so that i could fit between shields in close formation favoured by the Romans .The pilum, which had a triangular tip, would bend so it would be difficult to remove when it impaled the enemy so that they could not fight back. Their armor was cleverly designed so that the soldiers were not only very well protected, they could also move around quickly and easily, without excessive weight on their bodies, that would drag them down