Details The monument includes an enclosure castle situated on low lying land on the north bank of The Creek, near the west coast of the Isle of Sheppey. The castle survives as a low circular earthwork mound, c.100m in diameter and 1.5m high, surrounded by the partially infilled remains of a moat. This is visible to the north and south of the mound as an earthwork up to 0.6m deep and between 12m and 18m wide. To the east, the outer edge of the moat has been cut away by the construction of the railway line and to the west it has been completely infilled but survives as a buried feature. The early history of the castle is well documented, having been built by Edward III `for the defence of the realm and for the refuge of the inhabitants of the island' and named after Philippa, his queen. Its construction was started in 1361 and continued until 1369 with final touches, such as the outer gates, being finished between 1373 and 1375. The plan of the masonry structure is known from an Elizabethan manuscript and comprised a central well within a small, circular inner ward, c.18m in diameter, surrounded by a circular keep, 40m in diameter, with six outer circular towers. Beyond this was the outer ward, enclosed by a circular curtain wall with a main gate to the west and a small postern gate to the east. Pairs of high walls connected the main gate with the western face of the keep and the postern with the keep's gate. Each of these walls had a gateway in it. The moat then ran around the curtain wall and was crossed by two drawbridges at the gateways. In 1382 six of the towers collapsed owing to an earthquake and were rebuilt by Richard II. Various alterations and repairs were carried out until 1650, when the castle was declared obsolete by the Parliamentary Commissioners. The structure was demolished soon after. The well was reopened and deepened in 1725 and was retained in use until the 20th century with a second well sunk next to the first in 1868. In 1991 two shallow trenches were excavated in the north west corner of the site which located a cut likely to be the robber-trench where the stones of the outer curtain wall were removed after demolition. Excluded from the scheduling are the bus shelter, fences, brick walls, car park surface, standing buildings, tarmac road surface, pavement, rubbish bins and streetlamps, although the ground beneath all these features is included. Reasons for Designation Ringworks are medieval fortifications built and occupied from the late Anglo- Saxon period to the later 12th century. They comprised a small defended area containing buildings which was surrounded or partly surrounded by a substantial ditch and a bank surmounted by a timber palisade. Occasionally a more lightly defended embanked enclosure, the bailey, adjoined the ringwork. Ringworks acted as strongholds for military operations and in some cases as defended aristocratic or manorial settlements. Between the Norman Conquest and the mid-13th century, mainly during the 12th century, a number of motte and bailey castles and ringworks were remodelled in stone. In the case of ringworks, this could involve the replacement of the timber palisade surmounting the defensive bank with a thick stone wall to form a "shell keep". With only 200 examples recorded in England, ringworks are rare nationally and shell keeps constructed on ringworks are particularly rare with only 8 examples known to have been converted in this way. As one of a limited number and very restricted range of Norman fortifications, ringworks are of particular significance to our understanding of the period. Despite demolition of the above ground stonework in the 17th century and the construction of a pumping station, the site of Queenborough Castle survives comparatively well with buried features remaining largely undisturbed. It is the earliest example of a concentric circular castle in the country and is possibly the only royal castle to be constructed in the late medieval period. Partial excavation has demonstrated that the monument contains both archaeological remains and environmental evidence relating to the monument's construction, use and demolition.