Helepolis (Taker of Cities) is an ancient siege engine invented by Demetrius I of Macedon for besieging fortified places.

When Demetrius Poliorcetes besieged Salamis, in Cyprus, he caused a machine to be constructed, which he called The taker of cities. Its form was that of a square tower, each side being 90 cubits high and 45 wide. It rested on four wheels, each eight cubits high. It was divided into nine stories, the lower of which contained machines for throwing great stones, the middle large catapults for throwing spears, and the highest, other machines for throwing smaller stones, together with smaller catapults. It was manned by 200 soldiers, besides those who powered it by turning the large capstan driving the wheels via a belt.

At the great siege of Rhodes (305 BC/304 BC), Demetrius employed an helepolis of still greater dimensions and more complicated construction. Besides wheels it had casters, so as to admit of being moved laterally as well as directly. Its form was that of a large tapered tower. The three sides which were exposed to attack, were rendered fire-proof by being covered with iron plates. In front each story had port-holes, which were protected by shutters that could be opened or closed mechanically, and were made of skins stuffed with wool. Each story had two broad flights of steps, the one for ascending, the other for descending. On each level were various missile launching weapons such as ballistae and catapults, which were smaller in size, the higher the level. This helepolis was constructed by Epimachus of Athens; and a much esteemed description of it was written by Dioeclides of Abdera. It was no doubt the greatest and most remarkable engine of the kind that was ever erected.

Following the siege, the weapon was abandoned and the people of Rhodes melted down its metal plating and with the materials, built the Colossus of Rhodes.

In subsequent ages we find the name of helepolis applied to moving towers which carried battering rams, as well as machines for throwing spears and stones.