Mercia was one of the pre-Conquest Anglo-Saxon kingdoms of England.
Its centre was in the valley of the River Trent, and its tributaries, but later it grew to extend from the Hunber to the Thames, and west to the borders of Wales.
The kingdom roughly shook itself into shape around the later 6th century, and its first major line of kings were the descendants of Penda. In their wake came a line claiming descent from one Eowa, which included the Offa of Offa's Dyke, an early border marker between the Anglo-Saxon lands and those of the Welsh princes. Offa tried to secure his sucession by murdering many of the candidates. In the event this handed the kingdom, after the death of Offa's son Egfrith, to a rival line, that of Coenwalh. Within half a century Mercia had become a client kingdom of Wessex and in 919CE the kingdoms were merged.