St Illtyd's Church is located at the site of the oldest college in the United Kingdom, Cor Tewdws, which was founded c. 395 AD in honour of the Roman Emperor Theodosius I. It was refounded by St. Illtud c. 508 AD, from whom it derives its name. The current church building was built in the 11th century by the Normans, with portions being rebuilt in the 13th and 15th centuries. The church building is one of the oldest and best-known parish churches in Wales. It is a grade I listed building, or building of exceptional interest, and has been called both the 'Westminster Abbey of Wales' for its unique collection of carved stones and effigies, and 'the most beautiful church in Wales.'
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.