The hovering ram of Gera. Photo : Augusta Stylianou Artist

It was constituted by a protected scaffold on wheel and a ram which was suspended with ropes from its central beam. The rams were long wooden beams with metal heads that were used to demolish enemy walls. The operators pulled the ram backwards with the ropes and then released it. Thus the hovering ram struck the stones with force, breaking or overturning them. With the fluctuating ram suspension ropes, they managed to strike the wall on the desired target, beginning from the top
Sources:
Vitruvius, On Architecture X