One of the kingdoms of central Anglo-Saxon England; it held a position of dominance for much of the period from the mid-7th to the early 9th century. Mercia originally comprised the border areas (modern Staffordshire, Derbyshire, Nottinghamshire, and northern West Midlands and Warwickshire) that lay between the districts of Anglo-Saxon settlement and the Celtic tribes they had driven to the west. It later absorbed the Hwicce territory (the rest of West Midlands and Warwickshire, eastern Hereford and Worcester, and Gloucestershire) and spread also into what was later Cheshire, Salop, and western Hereford and Worcester. Mercia eventually came to denote an area bounded by the frontiers of Wales, the River Humber, East Anglia, and the River Thames. Its most famous kings were Penda (632-654), Aethelbald (reigned 716-757), and Offa (757-796). During this time the important Mercian School of manuscript illumination and sculpture developed. Thereafter it declined and disappeared under the encroachments of the Danes and of Wessex.