r. 757-796

Anglo-Saxon King

Ruler of Mercia, a kingdom in England, Offa left behind what is undoubtedly the third most well-known structure of pre-Norman Britain, after Stonehenge and Hadrian's Wall. Like the latter, Offa's Dyke is a line between one nation and its enemies. But whereas Hadrian intended his wall as a form of protection for Roman Britain—a purpose in which it failed miserably, as the fifth-century invasion of Offa's Anglo-Saxon ancestors made clear—Offa built his earthen dyke simply as a line of demarcation.

Offa's birth year is unknown, and his life prior to 757, when he became king of Mercia in southern England, is a mystery. Upon assuming the throne, he proceeded to bring southern England to the greatest degree of political unification and stability it had enjoyed since the Anglo-Saxon period began three centuries before.

When Offa's cousin Aethelbald (r. 716-757) was murdered, sparking a...