Old St Peter's Church is a ruined parish church in Thurso. It dates to at least 1125, and at one time was the principal church for the county, administered by the Bishops of Caithness.
Early in the 16th century, the vicarage of Thorso was held by Sir John Mathesoun chancellor of Caithness, on whose demission or otherwise Queen Mary in 1547 presented Master John Craig to the benefice. Master Walter Innes, who appears in record in 1554, was vicar of Thurso in 1560, and continued to hold the vicarage between 1561 and 1566. About 1567, John Rag was minister, and in 1574, Alexander Urquhart was minister of Olrik and Thurso, and John Davidsoun was reader at Thurso. In 1641, Alexander Monro, minister at Durnoch had from King Charles I, a grant of 800 marks Scots or of eight chalders victual in augmentation of his stipend from the rents of the bishopric in the parish of Thurso and elsewhere.
Old St Peter's, still standing, was disused since 1832 when a replacement church was built for the parish. That church, St Andrew's and St Peter's, is of Gothic style and was built to a design by William Burn.
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.