The old castle was largely rebuilt in the 19th century.
It was destroyed in 796, rebuilt by the crusaders in 1134 (their fortress and chapel remain, much ruined).
During the revolution of 1885 it was partly burned and was rebuilt on a somewhat larger plan.
Though the bishop's see was removed to Christiansand in 1685, the Romanesque cathedral church of St Swithun, founded by the English bishop Reinald in the end of the 11th century, and rebuilt after being burned down in 1272, remains, and, next to the cathedral of Trondhjem, is the most interesting stone church in Norway.
Victor (rebuilt1580-1615and 1795), to which is attached an ancient baptistery (dating from the 9th century but rebuilt in the 13th).