Haverfordwest Priory was a house of Augustinian Canons Regular on the banks of the Western Cleddau. The priory was first mentioned around 1200.
At the time of Henry VIII’s Dissolution of the Monasteries (1536–1541), it was acquired by Roger and Thomas Barlow, brothers of William Barlow, bishop of St David's.
From 1983 to 1996, the site (now under control of Cadw) was excavated and the outlines of the buildings are visible. Much architectural material of a high standard was discovered and can be seen in Haverfordwest museum. Also unearthed was a unique medieval garden with raised beds.
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.