The area was once part of the lands of the Cornovii, which consisted of the modern day counties of Cheshire, Shropshire, north Staffordshire, north Herefordshire and eastern parts of Powys. This was a tribal Celtic Iron Age kingdom. Their capital in pre-Roman times was probably a hill fort on the Wrekin. Ptolemy's 2nd century "Geography" names one of their towns as being Viroconium Cornoviorum (Wroxeter), which became their capital under Roman rule and one of the largest settlements in Britain. After the Roman occupation of Britain ended in the 5th century, the Shropshire area was in the eastern part of the Welsh Kingdom of Powys; known in Welsh poetry as the "Paradise of Powys". It was annexed to the Angle kingdom of Mercia by King Offa in the 8th century, at which time he built two significant dykes there to defend his territory against the Welsh or at least demarcate it. In subsequent centuries, the area suffered repeated Viking incursions, and fortresses were built at Bridgnorth (912) and Chirbury (913).