St Mary's Church (Mariakirken) was the royal chapel and had an important political role, as its provost from 1314 also was Chancellor of Norway. It was built originally in 1050 AD, but rebuilt and expanded several times. Final additions made in the 1300s. In the beginning of the 14th century, it was the third largest church in the country, and in the Middle Ages it was the royal chapel. The church was set on fire by Swedish forces in connection with an attack in 1523. After the Reformation, it was so dilapidated that it could not be repaired and was demolished in 1542.
Excavations were first conducted in 1867 under Nicolay Nicolaysen and later in the 1960s under the leadership of Håkon Christie. Remains of two people, deemed to be King Haakon V (1270-1319) and his Queen consort Euphemia of Rügen, were discovered during excavations of the ruins of the church and reinterred in the Royal Mausoleum in Akershus Castle.
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.