The first Archbishop of Canterbury was Saint Augustine of Canterbury who arrived in Kent in 597 AD, having been sent by Pope Gregory I on a mission to the English. He was accepted by King Æthelbert, on his conversion to Christianity, about the year 598. It seems that Pope Gregory, ignorant of recent developments in the former Roman province, including the spread of the Pelagian heresy, had intended the new archiepiscopal sees for England to be established in London and York. In the event, Canterbury was chosen instead of London, owing to political circumstances. Since then the Archbishops of Canterbury have been referred to as occupying the Chair of St. Augustine. (Wikipedia)
Little is known about the Anglo-Saxon cathedral, since a fire in 1067 destroyed most of it and centuries of building and re-building have made archaeological excavation difficult. In 1993, however, the renovation of the floor of the Nave and South Transept uncovered part of its foundations.