The area was covered first by Offa of Mercia, who constructed the dyke as a boundary to keep warring tribes out of the Mercian kingdom: an early indication of the ambivalent relations with the Welsh. The shire as an administrative unit was developed from Alfred the Great's Burghal Hidage, and the Shire-reeve courts of the Hundred. In 676, during the reign of King Æthelred of Mercia the Archbishop of Canterbury Saint Theodore of Tarsus founded the Diocese of Hereford, to minister to the minor sub-kingdom of Magonsaete, and he appointed Putta as the first Bishop of Hereford. The establishment of a centre of law and justice was supported by a monastic chapter that flourished during the Tenth century Reformation. Hereford's geographical location at the hub of the shire allowed Anglo-Saxon ealdormen to manage affairs; and Hereford played a vital role in the Scandinavian wars until Ralph, Earl Hereford was deposed by the regal Earl Harold Godwinson.