Situated on the banks of the River Adaja, San Segundo church was built in Caleno granite between 1130 and 1160. Before it was dedicated to St Segundo after the remains of the town's first Bishop were found in 1519, it had been dedicated to St Sebastian and St Lucia. The Bishop's remains were moved in 1615 with great pomp and ceremony to the chapel of St Segundo, which was built on to the apse of the Cathedral specifically as a final resting place.
The layout draws inspiration from the basilica style and has three naves and an upper end with three apses closed off with calotte and barrel vaults. Its slightly off-centre north-eastern orientation is probably due to the existence of an earlier church or an error made when the construction was being marked out. The southern porch has five archivolts set on columns and there are others of similar characteristics to the North and West, which were replaced in the 16th century. The structure of the naves was replaced in 1521 with a structure that shows Mudejar-style influences. Its current appearance is the result of refurbishment work that was carried out as from the 16th century.
The decoration with Romanesque sculptures is limited to a number of capitals with plant and figurative motifs. Inside, it boasts a sculpture of St Segundo in prayer by Juan de Juni.
There is a Roman altar stone opposite the west entrance that was found during recent archaeological work on the church.
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.