From the National Heritage List for England: Details The monument includes a motte and bailey castle dating from the years soon after the Norman Conquest, as well as the later remains of the curtain wall and the 13th century gatehouse. The principle feature of the earliest castle on the site is the earthen motte, circular in plan and 20m high. At its summit the motte measures 24m by 20m. Around the flattened top a wall was built to form a shell keep. The foundations of a number of buildings which backed onto the shell keep wall and a well were located during excavations in 1912 which resulted in the 7m wide depression visible today. The shell keep wall has been partially rebuilt in recent times to a height of ca.1m. The motte was originally encircled by a moat of some 14m width but this was infilled on the eastern side in the 12th century to ease access to and from the motte. Below the motte and to the east was a bailey, the line of which was consolidated by a tall stone curtain wall added in the 12th century which was in turn strengthened by a now-infilled outer moat on the east and north-east sides and to the south by the river. Inside the bailey the foundations of a number of buildings including a chapel are considered likely to survive. In the later 13th century, the original gatehouse was replaced with another with drum towers flanking a strongly-defended gateway. A wall-walk connected the new gatehouse with the keep. Many architectural details survive in the gatehouse, including sculpted windows and arrowloops. The Georgian buildings east of the gatehouse are excluded from the scheduling along with all service trenches, modern paths, steps and display boards, but the ground beneath is included. Reasons for Designation Motte castles are medieval fortifications introduced into Britain by the Normans. They comprised a large conical mound of earth or rubble, the motte, surmounted by a palisade and a stone or timber tower. In a majority of examples an embanked enclosure containing additional buildings, the bailey, adjoined the motte. Motte castles and motte-and-bai1ey castles acted as garrison forts during offensive military operations, as strongholds, and, in many cases, as aristocratic residences and as centres of local or royal administration. Built in towns, villages and open countryside, motte castles generally occupied strategic positions dominating their immediate locality and, as a result, are the most visually impressive monuments of the early post-Conquest period surviving in the modern landscape. Over 600 motte castles and motte-and-bailey castles are recorded nationally, with examples known from most regions. Some 100-150 examples do not have baileys and are classified as motte castles. As one of a restricted range of recognised early post-Conquest monuments, they are particularly important for the study of Norman Britain and the development of the feudal system. Although many were occupied for only a short period of time, motte castles continued to be built and occupied from the 11th to the 13th centuries, after which they were superseded by other types of castle. The castle at Tonbridge survives well despite the partial excavation of the motte top in the early 20th century and the adaptation of parts of the castle for Georgian residences. The diversity of features at the castle is high, including for example the architectural details of the gatehouse and the garderobe chutes in the curtain wall in addition to the shell keep. In addition the castle is well documented historically as a place frequented by royalty, which together with good public access and informative displays makes the castle of high amenity value.