the fortress lies under the foundations of York Minster, and excavations in the undercroft have revealed part of the Roman structure and columns. The Emperors Hadrian, Septimius Severus, and Constantius I all held court in York during their various campaigns. During his stay 207–211 AD, the Emperor Severus proclaimed York capital of the province of Britannia Inferior, and it is likely that it was he who granted York the privileges of a 'colonia' or city. Constantius I died in 306 AD during his stay in York, and his son Constantine the Great was proclaimed Emperor by the troops based in the fortress. In 314 AD a bishop from York attended the Council at Arles to represent Christians from the province. While the Roman colonia and fortress were on high ground, by 400 AD the town was victim to occasional flooding from the Rivers Ouse and Foss, and the population reduced. York declined in the post-Roman era, and was taken and settled by the Angles in the 5th century. Reclamation of parts of the town was initiated in the 7th century under King Edwin of Northumbria, and York became his chief city. The first wooden minster church was built in York for the baptism of Edwin in 627, according to the Venerable Bede. Edwin ordered the small wooden church be rebuilt in stone; however, he was killed in 633, and the task of completing the stone minster fell to his successor Oswald. In the following century, Alcuin of York came to the cathedral school of York. He had a long career as a teacher and scholar, first at the school at York now known as St Peter's School, founded in 627 AD, and later as Charlemagne's leading advisor on ecclesiastical and educational affairs. In 866, Northumbria was in the midst of internecine struggles when the Vikings raided and captured York. As a thriving Anglo-Saxon metropolis and prosperous economic hub, York was a clear target for the Vikings. Led by Ivar the Boneless and Halfdan, Scandinavian forces attacked the town on All Saints' Day. Launching the assault on a holy day proved an effective tactical move – most of York's leaders were in the cathedral, leaving the town vulnerable to attack and unprepared for battle. After it was conquered, the city was renamed from the Saxon Eoforwic to Jorvik. It became the capital of Viking territory in Britain, and at its peak