The Tribal Hidage is an important historical document. The oldest copies available were written in style of the 11th century. This is at a time when many of the names of the earlier regions had been forgotten. In some cases the list is the only evidence that a region or people of that name ever existed. There were probably older versions of the Tribal Hidage and may have dated back to when Penda of Mercia dominated Anglo-Saxon England (642–655).