St Mary, Chepstow, also known as Chepstow Priory is a parish church with an unusually long history, as some parts of the building are from the early 12th century, when it was the church of a Benedictine priory, established around 1072 by William FitzOsbern, 1st Earl of Hereford, who was also responsible for construction of Chepstow Castle, a few hundred feet west.
The most notable surviving component of the original building is the west doorway, framed by a multi-tiered semicircular arch, flanked by a pair of blind arches and set beneath a row of three arched windows, while much of the nave including the piers is also from this period, however the majority is much later, from the 18th and 19th centuries, and is not particularly elegant. The church is also of interest for several elaborate tombs and memorials, the best two being for Henry Somerset (died 1549), 2nd Earl of Worcester, and Margaret Cleyton (died 1627), a wealthy local benefactor.
The church is built on a slight rise in the middle of a bend along the River Wye, and it was for the last few centuries surrounded on all sides by closely-spaced buildings, though those to the south and west were cleared in recent times, and it now adjoins a carpark and the busy A48. The church is usually unlocked during the day, unstaffed, and is entered through a side door to the north.
Although Chepstow Priory was never very prosperous and was maintained by only a small group of monks, the church was large, and built to a high standard, mostly using the local yellow, Triassic-era Sudbrook sandstone, also seen at Chepstow Castle. The priory survived without major incident until the Dissolution of the Monasteries in 1536, soon after which all of the outbuildings (on the south and west sides) were demolished, including the chapter house and cloisters. The church was reduced in size and otherwise modified but the majority survived intact, and its management was transferred to the parish. The original (central) tower and the two transepts were destroyed during a storm in 1701, after which a replacement tower was installed at the west end, above the original Norman frontage. The eastern end of the building is of even more recent construction, following further modifications in 1841 and 1890.
The north doorway, within a small porch, opens into the nave, which is lined by five aisle-less bays that retain much of the Norman masonry. The bay just east of the entrance contains the colourful alabaster effigies of Henry Somerset and wife Elizabeth Browne, beneath an arched canopy. Nearby is a stone font from the 15th century. The nave leads to the original crossing and the two truncated transepts; that to the south houses the tomb of Margaret Cleyton, also depicting her two husbands and 12 children. Beyond is the choir and the altar, and all these sections are surrounded by 19th-century stonework. The church also contains a 17th-century pipe organ, originally installed in both Gloucester Cathedral and Bristol Cathedral. Another notable tomb is for Henry Marten (died 1680), a compatriot of Oliver Cromwell.