Mercia was an Anglo-Saxon kingdom located in the region now known as the English Midlands, including what is today the East Midlands and West Midlands of England. It was centered mainly on the valley of the River Trent and its tributaries. Its capital was Tamworth, now part of Staffordshire. Mercia was bordered by other Anglo-Saxon kingdoms such as Northumbria, Wessex, Sussex, Essex, and East Anglia, and to the west it bordered Welsh kingdoms like Powys and southern Wales. It was a dominant power among the Anglo-Saxons from the mid-7th to the early 9th century before eventually becoming a vassal kingdom under Wessex rule.