St. Hallvard's Cathedral (Hallvardskatedralen), the former Oslo Cathedral, was the earliest cathedral in Oslo. The cathedral was built at the height of the Old Town market square Oslo during the early 12th century, and was used as a church until about 1655. Besides being the bishop's seat and religious center of eastern Norway for about 500 years, the cathedral was the coronation church, royal wedding church, chapel royal, and one of Scandinavia's most visited place of pilgrimage. St. Hallvard cemetery is located mainly south of the cathedral. It was the honorary cemetery in Oslo and eastern Norway from around 1130 to 1639. Here the bishops, chiefs and other prominent men and women were buried. The most prominent was interred in the church along with the kings.
Today the cathedral is in ruins. The main body in the ruins park (Memorial Park), the southern part under a concrete cap - and the concrete lid of the street of Bispegata. Towards the end of the 19th century were Bispegata extended in an easterly direction, over the cathedral site. It has been put in place to remove Bispegata's eastern part, as a result of the completion of the Ekeberg Tunnel and the modified veian resort in the lower Lodalen. In that case, the ruins of St. Hallvard Cemetery exposed, and the Medieval city triangular marketplace, Oslo squares, re-established west of St. Hallvard Cemetery. Neighboring the Cathedral was the smaller Church of the Cross.
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.