For knowledge of the internal composition of the Kingdom of Mercia, we must rely on a document of uncertain age (possibly late 7th century), known as the Tribal Hidage – an assessment of the extent (but not the location) of land owned (reckoned in hides), and therefore the military obligations and perhaps taxes due, by each of the Mercian tribes and subject kingdoms by name. This hidage exists in several manuscript versions, some as late as the 14th century. It lists a number of peoples, such as the Hwicce, who have now vanished, except for reminders in various placenames. The major subdivisions of Mercia were as follows:
