OFFA REX ('King Offa') and, on the reverse side, Eð / IL / VA / Ld ('Ethilwald' - the moneyer who authorised the minting of the coin).
An English Emperor
Offa was a formidable ruler. As King of Mercia, he conquered the smaller but rich kingdoms of East Anglia and Kent, and exercised considerable influence over Wessex and Northumbria.
He was a contemporary of the great Frankish king Charlemagne and sought to stand up to him as an equal. He built Offa's Dyke - a 149 mile-long barrier - to shield his kingdom from the Welsh.
The portrait on this coin shows Offa in the style of a Roman emperor with an imperial diadem in his hair. This classical imagery greatly appealed to early medieval kings.
A standardised coinage
Offa reformed the Mercian coinage in the 760s to bring it into line with the new-style Carolingian penny. This broader, thinner silver coin became the standard denomination for some six hundred years. From now on all coins would carry the name of the ruler and the moneyer.
There was more coinage in circulation during the first half of the 8th century than there would be again until the 12th century, particularly around southern and eastern England. The same is true for the Low Countries. There seems to have been a short-lived surplus of silver in northern Europe, possibly from mines in Germany.
A trader's coin
These coins weighed the same as Charlemagne’s and could have traded internationally at the same value. In England, however, Offa prohibited the circulation of Carolingian and other foreign coins so that his coinage would dominate the currency.
In the second monetary reform of his reign, c.792, Offa increased the size, weight and hence value of the English penny, deliberately making it incompatible with the Frankish denier, at a time when Offa and Charlemagne were locked in a trade war.