Siege tower

A siege tower or breaching tower (or in the Middle Ages, a belfry) 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 to stand on top of the tower and shoot arrows into the fortification. Because the towers were wooden and thus flammable, they had to have some non-flammable covering of iron.

Used since the 11th century BC by the Babylonians and Assyrians in the ancient Near East, the 4th century BC in Europe and also in antiquity in the Far East, siege towers were of unwieldy dimensions and, like trebuchets, were therefore mostly constructed on site of the siege. Taking considerable time to construct, siege towers were mainly built if the defense of the opposing fortification could not be overcome by ladder assault ("escalade"), by mining or by breaking walls or gates.

The siege tower sometimes housed spearmen, pikemen, swordsmen, archers or crossbowmen who shot arrows and quarrels at the defenders. Because of the size of the tower it would often be the first target of large stone catapults but it had its own projectiles with which to retaliate.

Siege towers were used to get troops over an enemy curtain wall. When a siege tower was near a wall, it would drop a gangplank between it and the wall. Troops could then rush onto the walls and into the castle or city.

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