The monument includes the alien Benedictine Priory of St Mary, situated on level ground c.2km from the south bank of the River Thames. This includes the church, the cloister, east, west and south ranges, the reredorter and drain, the cemetery to the east of the church, the footings and foundations of asociated monastic buildings and the ground in between. Abbey Farm farmhouse is situated in the south west corner of the cloister and has incorporated the standing remains of the west range and the north and west walls of the frater. These lie to the south of the cloister garth, or courtyard, and are built of stone and flint up to 0.9m thick. Part of the south wall of the church is upstanding on the north side of the cloister garth and measures 0.7m thick, 4m long and 1.5m high. To the east are the buried foundations of the chapter house, warming house, rere-dorter and covered drains which were all noted during partial excavation in 1966. To the south of this area, chalk footings of other medieval monastic buildings have also been noted, all within the area of the precinct. The priory, originally built to house 16 nuns, was founded c.1148, when Mary, the daughter of King Stephen, became the first prioress. As an alien priory, St Mary's was originally dependent on St Sulpice, Rennes. This was the monastery from which Mary had come, bringing with her a number of the nuns. The priory, however, became independent at some time around 1227 when the King granted the priory a yearly fair at Michaelmas. The house was suppressed in 1521-2 when it was granted to St John's College, Cambridge. In 1965 a resistivity survey was undertaken in order to identify the position of any surviving foundations. The following year partial excavation of the site took place which revealed the plan of the medieval priory buildings. A stone coffin in the east alley of the cloister is the earliest datable evidence from the site, while a late 13th century brass jetton was found embedded in the mortar of a covered drain. None of the buildings can be dated unequivocally to the period of the founding of the priory, but some appear to have been built or possibly rebuilt in stone during the 13th century. Excluded from the scheduling are the occupied buildings, garden sheds, aviary, other outbuildings, gates, fences and fence posts, but the ground beneath all these features is included. ASSESSMENT OF IMPORTANCE A nunnery was a settlement built to sustain a community of religious women. Its main buildings were constructed to provide facilities for worship, accommodation and subsistence. The main elements are the church and domestic buildings arranged around a cloister. This central enclosure may be accompanied by an outer court and gatehouse, the whole bounded by a precinct wall, earthworks or moat. Outside the enclosure, fishponds, mills, field systems, stock enclosures and barns may occur. The earliest English nunneries were founded in the seventh century AD but most of these had fallen out of use by the ninth century. A small number of these were later refounded. The tenth century witnessed the foundation of some new houses but the majority of medieval nunneries were established from the late 11th century onwards. Nunneries were established by most of the major religious orders of the time, including the Benedictines, Cistercians, Augustinians, Franciscans and Dominicans. It is known from documentary sources that at least 153 nunneries existed in England, of which the precise locations of only around 100 sites are known. Few sites have been examined in detail and as a rare and poorly understood medieval monument type all examples exhibiting survival of archaeological remains are worthy of protection. St Mary's Priory survives comparatively well, with upstanding fragments of masonry as well as extensive below ground remains. Documentary sources, combined with the archaeological remains and environmental evidence demonstrated by partial excavation to be contained within the monument, provide an insight into the economy and way of life peculiar to a Benedictine priory.