After the battle of Nechtansmere, Mercia was, without doubt, the most powerful English kingdom.
Æthelbald, king of Mercia from 716 to 757, called himself ‘king of Britain’. He was later murdered by his bodyguard, which suggests that serious in-fighting was taking place. Then, when his successor King Offa 757 to 796 took to the throne, he oversaw an even greater expansion of Mercian power.
King Offa is probably best known for creating Offa’s Dyke, a 90-mile long earthwork marking the boundary between Mercia and Wales. This was probably in response to the increasing power of the kings of Gwynedd, who were also calling themselves ‘Kings of the Britons’ at the time Offa started calling himself ‘King of the English’. Offa most definitely dominated the other English kingdoms more successfully than previous kings, and he was even able to play a key role on the European stage.
The eighth century was a time of considerable prosperity for the country. This has been proven through excavations of the first towns that emerged after the retreat of the Romans – Southampton, London, Ipswich and York. The prosperity of the time was severely challenged by the arrival of the Vikings.