The Carmen de Hastingae Proelio (Song of the Battle of Hastings) is an early written source for the Norman invasion of England from September to December 1066, in Latin; attributed to Bishop Guy of Amiens, uncle to Count Guy of Ponthieu, who figures rather prominently in the Bayeux Tapestry as the vassal of Duke William of Normandy who captured Harold Godwinson in 1064.
The Carmen is generally accepted as the earliest known written account of the invasion, which naturally focuses on the famous Battle of Hastings. It is in poetic form, 835 lines of hexameters and pentameters, and is preserved only in a single extant copy (Bibliothèque royale de Belgique no. 10615-729, folios 227v-230v), which is apparently an early 12th century copy of the 11th century original.
Bearing all the signs of hasty work, the Carmen was most likely composed within months of the coronation of William as king of England (Christmas Day, 1066). Probably sometime in 1067, possibly as early as Easter of that year, to be performed at the royal festivities in Normandy, where King William I presided. The motivation for the poem's production and performance must have been something to do with Bishop Guy's family, which possibly was then out of favor over the involvement of Hugh of Ponthieu in the death of King Harold. For it is tempting to identify Hugh as the younger brother of Count Guy of Ponthieu, and the perpetrator of the mutilation of King Harold once he had been slain. For this reason, or some other unknown reason, Bishop Guy felt it necessary to impress King William with the contributions his nephew(s) had made to William's invasion of England. Also, at the time, Bishop Guy himself was out of favor with the pope, and perhaps wanted to garner some Norman influence by giving William the gift of the Carmen in his honor. A third possibility (though none of these is mutually exclusive), is the disfavor of Count Eustace of Boulogne, who appears by the contents of the Carmen, to have been a family friend (and or relative: most of these noble houses were intermarried by this time): therefore the Carmen might have been composed to put in a plug and reverse King William's banishment of Count Eustace following his failed invasion of England in the autumn of 1067 (Eustace remained in fact out of favor until late in the 1070s).
Altogether, the Carmen is the most vivid of the original written accounts, and practically the only one to give a non-Norman point of view in detail. (The Bayeux Tapestry is problematic; because we do not know the purpose of its creators, nor even for certain who they were; but it bears evidence of English involvement in its production.) In fact, it is the Carmen 's very vividness which has caused it in the past to come under attack as either a forgery, fraud or at the least a later, 12th-century source. But Frank Barlow has recently advanced convincing arguments to support the position of the Carmen as a very early source indeed, most likely from the year 1067.