side chambers. In 664 a synod was held at Whitby, Yorkshire, and differences between the Celtic and Roman practices throughout England were reconciled, mostly in favour of Rome. Larger churches developed in the form of basilicas, for example at All Saints' Church, Brixworth. The Romano-British populations of Wales, the West Country, and Cumbria experienced a degree of autonomy from Anglo-Saxon influence, represented by distinct linguistic, liturgical and architectural traditions, having much in common with the Irish and Breton cultures across the Celtic Sea, and allying themselves with the Viking invaders. This was however, gradually elided by centuries of English dominance. Characteristically circular buildings as opposed to rectangular, often in stone as well as timber, along with sculptured Celtic crosses, holy wells and the reoccupation of Iron Age and Roman sites from hillforts such as Cadbury Castle, promontory hillforts such as Tintagel, and enclosed settlements called Rounds characterise the western Sub-Roman Period up to the 8th century in southwest England and continue much later in independent Wales at post-Roman cities such as Caerleon and Carmarthen. Subsequent Danish (Viking) invasion marked a period of destruction of many buildings in Anglo-Saxon England, including in 793 the raid on Lindisfarne. Buildings including cathedrals were rebuilt, and the threat of conflict had an inevitable influence on the architecture of the time. During and after the reign of Alfred the Great (871–899), Anglo-Saxon towns (burhs) were fortified. Contemporary defensive banks and ditches can still be seen today as a result of this. Oxford is an example of one of these fortified towns, where the eleventh-century stone tower of St Michael's Church has prominent position beside the former site of the North gate. The building of church towers, replacing the basilican narthex or West porch, can be attributed to this late period of Anglo-Saxon architecture. 7th century In contrast to secular buildings, stone was used from very early on to build churches, although a single wooden example has survived at Greensted Church, which is now thought to be from the end of the period. Bede makes it clear in both his Ecclesiastical History and his Historiam Abbatum that the masonry construction of churches, including his own at Jarrow, was undertaken morem Romanorum, "in the manner of the Romans", in explicit contrast to existing traditions of timber construction. Even at Canterbury, Bede believed that St Augustine's first cathedral had been 'repaired' or 'recovered' (recuperavit) from an existing Roman