Originally, Beowulf tended to be dated as closely as possible to the events it describes. Hygelac, who is Beowulf's uncle and king of the Geats, is killed leading a raid against the Frisians (1202ff). This is the Danish king who Gregory of Tours records in the Historia Francorum (III.3) as being killed leading a sea raid against the Franks. The raid can be dated to about AD 520 and the date of the poem, itself, has been attributed to the mid-sixth century. But such an early date does not presuppose the Christian audience of Beowulf.
In the Ecclesiastical History (IV.24), Bede relates how the monks at Whitby would improvise verses, passing the harp as each recited songs to entertain the group. Indeed, Alcuin (Letter 160) complains about pagan songs being enjoyed by monks and asks in exasperation "What has Ingeld to do with Christ?" (Ingeld, who is betrothed to Hrothgar's daughter, is another figure who appears in Beowulf, 2065.) Caedmon, an illiterate lay brother at the monastery, would leave the table when it was his turn to sing and yet, says Bede, it was he, hearing the words in a dream, who first composed "poetry in his own English tongue," adapting the heroic language of traditional Germanic verse to a Christian subject.
The abbess at the time was Hilda, who died in AD 680. Beowulf, then, would have to be composed sometime later, after Caedmon and however long enough after the conversion of the English for the Christian usage and Biblical allusions in the poem to be appreciated by its audience. This argues for a date sometime in the early eighth century, probably in a monastic context, since literacy would largely have been restricted to the clergy.
Lindisfarne was sacked in AD 793, and it seems improbable that a poem praising the Danes would be written after the Viking raids of the late eighth and early ninth century. The poems of Cynewulf, which were written at about the same time, also show a familiarity with Beowulf, which would seem, therefore, to have been composed sometime between AD 680 and AD 800.
Date and place of composition are closely related and, if Beowulf was composed early in the eighth century, then Northumbria in the age of Bede would be the likely location; if late in the century, then Mercia and the court of Offa, especially since Offa, an ancestor of the royal house, is characterized as being "honoured far and wide for his generous ways, his fighting spirit and his far-seeing defence of his homeland" (1957ff).