Offa (died July 26, 796) was a King of Mercia (757 - 796). Prior to the rise of Wessex in the 9th century, he was arguably the most powerful and successful of the Anglo-Saxon kings. He effectively ruled the whole of England south of the River Humber during the latter part of his reign.
Offa was the son of Thingfrith and a descendant of Eowa, the brother of King Penda, who had ruled over a hundred years before. Following the murder of his cousin, King Ęthelbald in 757, Offa defeated and exiled Beornrad, Ęthelbald's successor, thus seizing the throne of Mercia. Offa took over a kingdom that had enjoyed supremacy over southern England during Ęthelbald's reign, but this supremacy had been seriously weakened by Ęthelbald's death and the subsequent internal conflict. Offa thereafter endeavored to reestablish Mercian power over the other Anglo-Saxon kingdoms.
For much of his reign, Offa struggled to assert his authority over the Kingdom of Kent. By 764, it was under his influence, for it was then that he installed a client king there, Heaberht. By 772, however, Offa was attempting to rule Kent directly. This provoked a rebellion under another former client king, Egbert, and a battle was fought at Otford in 776. The outcome was not recorded, but since Offa does not seem to have exercised any authority over Kent during the years that immediately followed the followed the battle, we may consider it likely that it was a Mercian defeat. Offa reestablished his authority over Kent with a subsequent and successful invasion around the year 785, however, and ruled it directly for the remainder of his life.
In Sussex, Offa's authority appears to have been recognized early by the local kings of its western part, but eastern Sussex does not seem to have submitted to him so readily. In 771, a war was fought which ended in Offa's imposition of his rule over the whole of Sussex by 772; the South Saxon kings were afterward known merely as "dukes".
Elsewhere in England, Offa won an important victory over the West Saxon king Cynewulf at the Battle of Bensington (in Oxfordshire) in 779, reconquering land that had earlier been lost to the West Saxons. In 786, after the murder of Cynewulf, Offa intervened to place Beorhtric on the West Saxon throne, possibly in opposition to a rival claimant, Egbert. During Beorhtric's reign, he clearly recognized Offa as his overlord, and he married Eadburh, a daughter of Offa, in 789.
In 794, Offa took over East Anglia after the murder of its king, Aethelbert. The killing was generally attributed to the treachery of Offa, although according to one version of the story, Aethelbert's death was the work of Offa's wife, Cynethryth.
Like most Mercian rulers of the period, Offa was often in conflict with the various Welsh kingdoms. There was a battle between the Mercians and the Welsh at Hereford in 760, and Offa is recorded as campaigning against the Welsh in 778, 784 and 796. He is perhaps best known for Offa's Dyke, a great earthen wall between England and Wales. However, although this landmark is named after him, it is not known with certainty to what extent he was responsible for its construction. Some attribute the building of all or parts of the dyke to earlier periods.
He introduced silver coinage in England, producing the first English silver pennies, as well as a copy of the gold dinar of the Abbasid caliph Al-Mansur dated 157AH, which differs from the original by adding the inscription OFFA REX. Since this coin contains the Arabic profession of faith in Allah, it has been cited by some as proof that Offa had converted to Islam. However, it is infinitely more likely that the coin was produced in order to trade with Islamic Spain, and the king, his engravers, and officials, simply copied the Arabic coin without any comprehension of what the inscriptions said (particularly considering that "OFFA REX" is upside down in relation to the Arabic script, and the word "year" is misspelled in Arabic). Offa's coins also sometimes featured the image of Cynethryth.
Although Offa had initially used the title "rex Merciorium" (king of the Mercians), his titles became more grandiose as his reign progressed. In 774, he is first recorded as using the title "rex Anglorum": king of the English. He was thus the first king to use that title, a sweeping statement of his power.
In his relations with the most powerful European ruler of the age, the Frankish king Charlemagne, it is clear that the latter recognized Offa's power and accordingly treated him with respect. It is also evident, however, that Offa wanted to be treated not merely respectfully, but as an equal of Charlemagne, and this insistence produced some discord in his relations with the Franks. Around the year 789, Charlemagne attempted to negotiate the marriage of one of his sons to one of Offa's daughters; Offa, however, made such an arrangement contingent upon the marriage of his own son, Ecgfrith, to one of Charlemagne's daughters. Charlemagne considered this demand a serious affront, and responded by temporarily closing Frankish ports to traders from England.
Offa came into conflict with Jaenbert, the Archbishop of Canterbury, and he tried to reduce the power of Canterbury through the establishment of a rival archdiocese at Lichfield, obtaining the approval of Pope Adrian I. A council at Chelsea agreed to its creation in 787, although only after some dispute. Hygeberht was made the first (and only) archbishop of this new see.
In his authoritative history, Anglo-Saxon England, Sir Frank Stenton argued that Offa was perhaps the greatest king of the Anglo-Saxon kingdoms, but that the proof of his abilities was obscured by the lack of a historian (such as Bede a half-century earlier, or Asser a century later) to describe his achievements. "No other Anglo-Saxon king ever regarded the world at large with so secular a mind or so acute a political sense," wrote Stenton.
During the last decade of his reign, Offa exerted himself to ensure that his son Ecgfrith would succeed him. In 787, he had Ecgfrith crowned as his co-ruler. After Offa's death in July 796, however, Ecgfrith survived for only five months, dying under unclear circumstances. Offa's reign marked the apogee of Mercian power: only a quarter of a century after his death (825), the role of leading English power passed to Wessex.