The Church of San Xoán (or Saint John) of Portomarín is an unusual Late Romanesque temple as it is designed to be both a church and a castle and so has architectural characteristics of both buildings. As a church it has one barrel vaulted nave, a semicircular apse and all the typical decorations of Romanesque churches; these include a carved portal with archivolts, rose windows and carved capitals. As a castle its perimeter is surrounded by merlons, it has four defense towers (one at each corner) while behind it lies an adarve, a defensive street. The north west tower currently has a stork's nest with two young (2011). The church was relocated to its current position from the valley in the 1960s when the river was flooded to form a reservoir.
It is situated on the principal route of the Way of St. James to Santiago de Compostela, where other Templar and Knight Hospitaller churches and castles were constructed as a result of the effort of the Hospital Orders to protect the way to the tomb of Santiago; others include the churches of Torres del Río, Eunate and the Castle of Ponferrada.
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.