The hexagonal Great Tower was probably begun in the 1430s and 1440s, possibly on the motte of a previous castle. The tower today has lost not only one of its walls but part of its upper structure, and would originally have been three storeys high with probably additional machicolations on top similar to those on the gatehouse. It was designed to be a self-contained fortification, with its own water and food supplies, and luxurious quarters lit by large windows on the upper floors. Originally the tower was reached by a bascule drawbridge, usually considered to be drawn from contemporary French designs, such as those at Ferté-Milon and Vannes. This drawbridge was designed to have two parts—a wide, heavy bridge that would be raised or lowered when the family was in residence, and a thinner bridge, easier to lift, designed for the use of servants at other times. The Herberts used the bridge as their badge, and it can be seen in the carved window designs around the castle. The drawbridge was replaced with a grander stone bridge in the 1460s, probably at a cost of around £900 to £1000. An apron wall with six turrets was also added around the tower at around the same time.