Helepolis

Helepolis (Greek: ἑλέπολις, English: "Taker of Cities") is the Greek name for a movable siege tower.

The most famous was that invented by Polyidus of Thessaly, and improved by Demetrius I of Macedon and Epimachus of Athens, for the Siege of Rhodes (305 BC). Descriptions of it were written by Diodorus Siculus,Vitruvius, Plutarch, and in the Athenaeus Mechanicus.

The Helepolis was essentially a large tapered tower, with each side about 130 feet (41.1 m) high, and 65 feet (20.6 m) wide that was manually pushed into battle. It rested on eight wheels, each 15 feet (4.6 m) high and also had casters, to allow lateral movement as well as direct. The three exposed sides were rendered fireproof with iron plates, and stories divided the interior, connected by two broad flights of stairs, one for ascent and one for descent. The machine weighed 160 tons, and required 3,400 men working in relays to move it, 200 turning a large capstan driving the wheels via a belt, and the rest pushing from behind. The casters permitted lateral movement, so the entire apparatus could be steered towards the desired attack point, while always keeping the siege engines inside aimed at the walls, and the protective body of the machine directly between the city walls and the men pushing behind it.

The Helepolis bore a fearsome complement of heavy armaments, with two 180-pound (82 kg) catapults, and one 60-pounder (27 kg) (classified by the weight of the projectiles they threw) on the first floor, three 60-pounders (27 kg) on the second, and two 30-pounders (14 kg) on each of the next five floors. Apertures, shielded by mechanically adjustable shutters, lined with skins stuffed with wool and seaweed to render them fireproof, perforated the forward wall of the tower for firing the missile weapons. On each of the top two floors, soldiers could use two light dart throwers to easily clear the walls of defenders.