Built in the 12th century by Pedro Álvarez de Soutomaior it is one of the most important castles in Southern Galicia. Its origins can be traced back to the reign of Alfonso VII, when a military construction was built in a strategic location in the town of Soutomaior. On a hill at 119 metres above sea level at the bottom of the Ría de Vigo, the castle was near the coast but protected against the sea incursions of the Normans, the Turkish or pirates. It also controlled the communications from north to south, and dominated the valley of the Verdugo River, from its confluence with the Oitavén River to its mouth.
In the 15th century, the defensive tower was turned into a two-walled complex. At that time, the castle was closely linked to Pedro Álvarez de Sotomayor, popularly known as Pedro Madruga, who held the title of Count of Camiña, Viscount of Tui, and Mariscal of Baiona. There seems to be evidence that Cristopher Columbus and Pedro Madruga were the same person, since they had friends and rivals in common, and about one hundred places discovered in the New World were renamed with place names from As Rías Baixas.
Over history, Soutomaior was the centre of feudal power, the setting of many battles, and the summer residence of the noble families. Today, it is a historic site open to the public with a garden recognised as an International Garden of Excellence. The current magnificence of the building has been the result of several renovations and alterations.
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.