Fonmon Castle

The origins of Fonmon Castle are poorly documented, and most of its early history has been recovered from the fabric rather than from records. A popular story holds that it was raised by Oliver St John of Fonmon, one of the Twelve Knights of Glamorgan who effected the Norman conquest of Glamorgan; that tale has since been shown to be legendary, given its credence by a "historic" account written by Sir Edward Stradling in the 1560s.

A timber fortification is thought to have been put up on the site soon after the Norman invasion of Wales, with stonework added around 1200. The thick walling to the left of the entrance is identifiably 12th-century in design and marks a small rectangular keep of roughly 8 m by 13 m. In the 13th century a curtain wall was carried from the east side of the keep towards a steep scarp, followed by a much larger L-shaped range to the south with a tower at the south-eastern angle. The castle's thickest walls run along the ravine edge to the east, which is a curiosity, since that was the hardest side to attack; some further defence is therefore thought to have covered the more open south and west approaches.

These early works are attributed to the St John family, associated with the castle through the Middle Ages and its owners until 1656. Oliver St John's marriage, placed somewhere between about 1394 and 1437, was to Margaret Beauchamp, grandmother of Henry VII, tying the house to the Tudor line. The next major addition waited until the 16th century: a short north wing built over a barrel-vaulted semi-basement.

The castle survived being damaged during the English Civil War, the St Johns having taken the Parliamentarian side. Soon afterwards the family fell into financial difficulties and had to sell their Glamorgan estates, Fonmon going to the Parliamentarian officer Colonel Philip Jones.

Jones is believed to have improved the rooms of the east range and added a double-depth wing on the north side, though he retired from public life at the Restoration. On his death the castle passed to his son Oliver, who held it from 1678 to 1685. Philip Jones's grandson, Robert Jones I, assembled a notable collection of paintings, among them a portrait of the family by William Hogarth, now in the National Museum in Cardiff.

The next great remodelling came under Oliver's great-grandson Robert Jones III (1738-93), who married Jane Seys, heiress to the Seys of Boverton. From 1762 the couple employed Thomas Paty of Bristol, adding render and battlements to give the house more of the appearance of a castle. The battlemented watch tower south of the house, absent from the estate plan of 1622 but present on those of 1770, is assumed to belong to the same medievalizing improvements. The library ceiling is the work of the Bristol plasterer Thomas Stocking, and is reckoned the best rococo plasterwork in Wales.

The estate went into decline through the 19th century, and little was done to the castle beyond the entrance porch and an extension to the south wing between 1840 and 1878. With the end of the Jones dynasty the castle passed by marriage in 1917 to Sir Seymour Boothby, one of the Boothby baronets. In 2019 Nigel Ford acquired the castle and some 350 acres of the remaining estate, and an extensive wilding project has since begun to improve the biodiversity of the ground; as of 2024 the park is also host to archery, axe throwing and other outdoor activities.

Fonmon, in the community of Rhoose, is a Grade I listed building and a National Monument of Wales, and its gardens are designated Grade II on the Cadw/ICOMOS Register of Parks and Gardens of Special Historic Interest in Wales; the watch tower was listed separately at Grade II* in 1952. Drastically remodelled in the 18th century but never Gothicized, it is counted a great architectural rarity.

In early 2024 a cemetery of the 6th or 7th centuries was uncovered in a field on the castle grounds. By 2025 the graves of 39 adults and 2 children had been excavated; most of the skeletons are female, and some graves held shards of pottery and fine etched glass. Further digging exposed an Iron Age settlement, in whose entrance ditch the skeleton of a dog, radiocarbon-dated to 700-500 BC, had been placed deliberately, perhaps as a symbolic guardian.