Towering high above the walls, the towers on a castle are perhaps one of the most distinguishing features. After all, the castles of the high middle ages were, in effect, simply a series of towers connected by walls (the keep being considered the castle's primary tower). Towers served many purposes: They were used as lookout posts for watchmen, as a support bases for structures such windmills or siege engines, or simply for storage of materials such as arsenal or food. All these functions however were somewhat trivial next effectiveness of the mural tower in defense against siege.
The primary defensive function of the tower was inherited from the Romans. By projecting from the wall, the mural tower (otherwise known as the flanking tower) allowed flanking fire to be cast upon the enemy. It also provided effective cover over the curtain wall should the enemy have tried to reach it by escalade.
Running around the outside of the tower, just down from the top were putlog holes as there were on the walls. Timber beams slid into these holes and supported a wooden overhanging gallery known as hoarding. Hoarding was built all along the top of the towers and walls before a siege, allowing better command (more effective defense) over the castle's outer foundation. From inside the hoarding materials could be dropped or shot directly down upon the enemy.
Toward the end of the 13th century, permanent stone hoarding became increasingly common as wooden hoarding was easily set on fire by flaming projectiles (despite the watered down hides that often covered their roofs). These projecting masonry parapets were supported on stone brackets called corbels, thus replacing the wooden putlogs used in temporary hoarding. Between each corbel was open to the wall-walk forming a machicolation, through which offensive materials were dropped.