Church of St. Teilo was probably built at the end of the 12th century or the beginning of the 13th century. During the Middle Ages, Llantilio Crossenny was the seat of the Llandaff bishops, which resulted in the extraordinary scale of the extension of the temple. In the fourteenth century, the chancel was rebuilt and a northern chapel and a western porch were added. In the 15th century, the nave of the church was rebuilt in the English Perprndicular Gothic style. In 1708, a spire was added to the tower, and the windows of the southern aisle were modernized in 1857, during the Victorian renovation.
The church was built of red sandstone. In the fourteenth century it consisted of a nave with two side aisles in the form of a four-bay basilica, a four-sided tower on the eastern side of the nave, flanked from the north and south by the arms of the transept, and a spacious, rectangular chancel. In the same century, the northern arm of the transept was rebuilt and enlarged into a great rectangular chapel, while the west façade was preceded by a porch. Also the southern arm of the transept had an eastern chapel, probably originally equipped with a room on the upper floor.
Originally, the church was illuminated by narrow, long, lancet windows, pierced in the west façade and probably also in the aisles. The eastern side of the church was finished with a chancel with a single, large, Gothic window filled with a three-light tracery. Centrally located at the crossing, the tower received a two-light windows on each side, with every opening topped with a trefoil. In the 15th century, some of the windows, especially in the side chapels, were equipped with late Gothic windows.
Inside, the nave was separated from the aisles by relatively simple but elegant pointed, moulded arcades, based on six octagonal pillars. A similar, only much lower arcade led to the undertower space and another to the chancel, which was opened onto the northern chapel with a large arcade and a diagonal passage in the thickness of the wall facing the altar (squint). All parts of the church were topped with an open roof truss and wooden ceilings.
The church at Llantilio Crossenny is one of the most magnificent medieval sacral buildings in Wales, both because of its excellent state of preservation and the remarkable scale of construction, contrasting with the small town. Only the windows of the aisles and the clerestory were mostly replaced during the 19th-century renovation. The church still performs sacral functions, but it is also open to visitors.
Salter M., The old parish churches of Gwent, Glamorgan & Gower, Wolverhampton 2002.
Wooding J., Yates N., A Guide to the churches and chapels of Wales, Cardiff 2011.
Website britishlistedbuildings.co.uk, Church of St Teilo A Grade I Listed Building in Llantilio Crossenny, Monmouthshire.