Kärkna Abbey, now ruined, was a former Cistercian monastery in Estonia. The monastery was founded before 1233 by the Bishop of Dorpat, Hermann von Buxhoeveden, and settled by monks from Pforta Abbey, of the filiation of Morimond. An early destruction by heathen inhabitants of the district is mentioned in 1234. After attacks by Russian forces from the principality of Vladimir-Suzdal and the Novgorod Republic it was rebuilt in about 1240 as a fortress surrounded by a moat and a rectangular granite wall. In 1305 it was placed under Stolpe Abbey on the Peene in Pomerania, which had joined the Cistercian order the previous year. In August 1558 the monastery was destroyed at the beginning of the Livonian War. There are remains of the foundations and of the perimeter walls.
The rectangular church was about 47 metres long, and consisted of a single nave of five vaulted bays. Unusually for a Cistercian church it also had a crypt of 10 bays containing two aisles, which was used not only as a place of burial but also as a place of shelter during hostilities. To the south of the church were attached the conventual buildings in the usual form of three ranges arranged in a square round a cloister and a central courtyard, with the chapter house in the east range.
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.