Which device was primarily used to breach walls during a siege?

The correct answer is the aries, also known as the ram. This ancient siege engine was specifically designed to breach walls or gates during attacks. Typically, it consisted of a large beam with a heavy bronze or metal head, which could be swung back and forth to create sufficient force to break through fortifications.

The design of the aries made it effective for its purpose, allowing construction teams to get close to enemy walls and apply focused pressure. This effectiveness in breaching walls made it a key component of siege warfare in ancient times.

The other devices listed, while used in warfare, served different primary functions. The onager was a type of catapult used to hurl projectiles over walls rather than breach them directly. The scorpio was a smaller crossbow that fired bolts, effective for defense but not for breaching walls. The ballista operated similarly to a giant crossbow or catapult, used to launch projectiles rather than to penetrate walls. Each of these devices had its own specialization in siege warfare, but the aries stands out as the dedicated tool for breaking through fortifications.