Helepolis is the Greek name for a movable siege tower.

A Roman siege tower or breaching tower is a specialized siege engine, constructed to protect assailants and ladders while approaching the defensive walls of a fortification. The tower was often rectangular with four wheels with its height roughly equal to that of the wall or sometimes higher to allow archers or crossbowmen to stand on top of the tower and shoot arrows or quarrels into the fortification. Because the towers were wooden and thus flammable, they had to have some non-flammable covering of iron or fresh animal skins.