St Cadwaladr's Church is a Grade I listed church in Llangadwaladr, Anglesey. The church is built in the perpendicular style. The nave is dated to the 12th to early 13th century and the chancel to the 14th. Considerable additions were later made in the mid 17th century, with the north chapel in 1640 and the south chapel in 1661. In 1856 the church underwent restoration, at which time to south porch was added.
In the newer part of the churchyard, south of the church, are war graves of four British airmen and a Polish airman of World War II.
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.