The church of St. Peter, Paul and John in Llantrisant was founded in the 14th century. In the fifteenth and sixteenth centuries, it was significantly expanded, among others, a tower was erected at that time and the porch. The date of 1593 engraved in the nave, means rather royal visit, than the next reconstruction. Victorian renovation the church passed in the second half of the nineteenth century.
The medieval church consisted of a wide nave on a rectangular plan, a narrower and shorter chancel, also on a rectangular plan, a massive, four-sided tower on the west side and a southern porch. The tower was topped with a decorative battlement and received a communication turret on the south-eastern side. On the south side of the nave there was an avant-corps, which probably housed the internal stairs to the rood screen floor, separating the nave from the chancel inside. The original, 14th-century windows were probably not very large, pointed, topped with trefoils. At the end of the 15th century, some of them were enlarged in the late Gothic style. In the center, on the southern wall of the choir, there was a large piscina placed with a canopy topped with a trefoil.
The church avoided major early modern interference with the body of the building, keeping the medieval layout. Most of the windows were renovated or replaced in the 19th century. A late-medieval window with a tracery is located in the eastern wall of the chancel, and a window from the beginning of the 14th century in the southern wall of the chancel. The piscina inside the building has also survived.
Salter M., The old parish churches of Gwent, Glamorgan & Gower, Wolverhampton 2002.
Website britishlistedbuildings.co.uk, Church of Saints Peter, Paul and John A Grade I Listed Building in Llantrisant Fawr, Monmouthshire.