It is a history book. The early history of Hereford, like that of the majority of cathedral churches, is veiled in the obscurity of doubtful speculation and shadowy tradition. Although the see had existed from the sixth century, it is not till much later that we have any information concerning the cathedral itself. From 755 to 794 there reigned in Mercia one of the most powerful and important rulers of those times, — King Offa. He was a contemporary of Charles the Great, and more than once these two sovereigns exchanged gifts and letters. Under Offa Mercia became the first power in Britain, and in addition to much fighting with the West Saxons and the Kentish men he wrested a large piece of the country lying west of the Severn from the Welsh, took the chief town of the district which was afterwards called Shrewsbury, and like another Severus made a great dyke from the mouth of the Wye to that of the Dee which became henceforth the boundary between Wales and England, a position it has held with few changes to the present day. In church history Offa is of no less importance than in secular, for as the most powerful King in England he seems to have determined that ecclesiastical affairs in this country should be more under his control, or at least supervision, than they could possibly be with the Mercian church subject to the Archbishop of Canterbury. In 786, therefore, he persuaded the Pope to create the Archbishopric of Lichfield. Although Canterbury regained its supremacy upon Offa's death when Lichfield was shorn by a new Pope of its recently acquired honours, the position gained for the latter see by Offa, though temporary in itself, must have had lasting and important influence. Offa is generally held responsible for the murder, about 793, of Æthelberht, King of the East Angles, who had been promised his daughter, Æthelthryth, in marriage.