Ancient kingdom, central England. One of the Anglo-Saxon kingdoms of the Heptarchy, it comprised the border areas, corresponding to modern Staffordshire, Derbyshire, Nottinghamshire, and northern West Midlands and Warwickshire. Offa, who ruled from 757 to 796, created a single state from the River Humber to the English Channel. After Offa's death, Mercia declined, overshadowed by Wessex. In 877 the Danes divided Mercia into English and Danish sections. After the reconquest of the Danish lands in the early 10th century, it came under the rule of Wessex.