St Mary's Church, Llanfair-yng-Nghornwy is a medieval parish church in the north-west of Anglesey, north Wales. The date of foundation of the church, which is in the village of Llanfair-yng-Nghornwy, is unknown, but the oldest parts date from the 11th or 12th century. It has twice been enlarged: in the 15th century, when the chancel was rebuilt, and in the 16th century, when a chapel was added to the south of the chancel, separated by three arches. The tower at the west end is from the 17th century. A south porch of unknown date has been converted into a vestry, and the church is now entered through the tower.
The church is still used for worship by the Church in Wales, one of nine in a combined parish, although as of 2013 there has not been an incumbent priest since September 2009. People associated with the church include James Williams, a 19th-century rector who was awarded a gold medal for his efforts to save lives at sea, and his great-grandson, the artist Sir Kyffin Williams. Both are buried in the churchyard.
References:The Church of St Donatus name refers to Donatus of Zadar, who began construction on this church in the 9th century and ended it on the northeastern part of the Roman forum. It is the largest Pre-Romanesque building in Croatia.
The beginning of the building of the church was placed to the second half of the 8th century, and it is supposed to have been completed in the 9th century. The Zadar bishop and diplomat Donat (8th and 9th centuries) is credited with the building of the church. He led the representations of the Dalmatian cities to Constantinople and Charles the Great, which is why this church bears slight resemblance to Charlemagne's court chapels, especially the one in Aachen, and also to the Basilica of San Vitale in Ravenna. It belongs to the Pre-Romanesque architectural period.
The circular church, formerly domed, is 27 m high and is characterised by simplicity and technical primitivism.