Guarding a crossing over the River Medway, the important castle of Tonbridge was founded by Richard Fitz Gilbert. It existed by 1088, when Rufus stormed the castle with the help of a native English army raised to quell the rebellion of Bishop Odo of Bayeux. Despite his involvement in this revolt, Fitz Gilbert retained possession.
The castle is an impressive example of a Norman motte and bailey - a layout curiously rare in Kent. On top of the great motte are the lower courses of a round shell keep. The bailey curtain dates from thirteenth century, probably from the time of the earlier Gilbert de Clare or his son, Richard. Owing to later stone robbing, it is now very ruinous and none of the flanking towers survive. The curtain is best preserved where it overlooks the river, four latrine chutes showing that residential buildings once stood here.
The Red Earl's gate house, by contrast, is still an imposing structure. Newly built in 1275, when Edward I visited the castle, the gatehouse is an outstanding example of Edwardian military architecture. Massive U-fronted towers, rising from square bases, flank the long entrance passage, which was protected by two portcullises, two pairs of gates and three rows of murder holes in the vault. Circular stair turrets clasp the rear corners.
The building is a classic example of a keep-gate house, which could be defended independently if the rest of the castle fell. Hence the inner gates barred access from the bailey and portcullises sealed off even the doors leading to the curtain wall walks. A hall occupied the whole of the second floor of the gatehouse. This awkward arrangement was necessary, since the chamber immediately over the gate passage would be clogged with drawbridge and portcullia winding gear. An eighteenth century house stands beside the gatehouse.