The Category A listed Holy Trinity is the most historic church in St Andrews. The church was initially built on land, close to the south-east gable of the Cathedral, around 1144, and was dedicated in 1234 by Bishop David de Bernham. It then moved to a new site on the north side of South Street between 1410–1412 by bishop Warlock. Much of the architecture feature of the church was lost in the re-building by Robert Balfour between 1798–1800. The church was later restored to a (more elaborately decorated) approximation of its medieval appearance between 1907–1909 by MacGregor Chambers.
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.