The site of the present city was tidal and swampy, ut the ford by the high ground, where the cathedral now stands, was of great importance, for here was the first sure crossing of the tidal river for many a mile. Sometime before AD655, a small mission church was built within the former Roman enclosure and houses and merchants clustered around. Later, alongside it, was built the first cathedral and in 680 Bosel, a monk from St Hilda's Abbey in Whitby was sent to become the first Bishop of Worcester.
For the next three-and-a-half centuries Worcester was harried by invaders, mostly by the Danes coming up the Severn. In Alfred's time, the first walls to defend the lower settlement were built; in Norman times BBishop Wulstan built his great cathedral where Oswald's church had stood, and alongside it, the Norman sheriff raised the castle mound to guard the ford. So began the city of Worcester, by medieval times the fifth most important city in the land; but on the high ground to the east there still stood the old quadrilateral fortress, two and a half miles from Crookbarrow to Elbury, and three miles from the round hill at Spetchley to the cathedral tump at the river ford.