Zelená Hora ('Green Mountain') is a castle on the north side of Nepomuk. The church has been a pilgrimage site since the 1700s. There was originally a fortified church built in the late 14th century. It was forfified probably in 1419-1420 during Hussite Wars.
The current castle was built in 1669-1696 by Šternberk family in Baroque style. In 1819 Václav Hanka's forged medieval Manuscript of Zelená Hora, a counterpart to his Manuscript of Dvůr Kralové, was allegedly discovered in the castle and not exposed as a literary hoax, by Atheneum, until 1886.
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.