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).
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.
The fortress was rebuilt, and after 280 served the Aetolians as a bulwark against Celts and Macedonians.
The principal palace was the Chehel Situn (forty pillars), destroyed by the Afghans in 1723, and, although rebuilt by Nadir Shah in 1731, already in ruins in 1743.
