Brewer's: Song of Roland
the renowned nephew of Charlemagne, slain in the pass of Roncesvalles. At the battle of Hastings, Taillefer advanced on horseback before the invading army, and gave the signal for onset by singing this famous song.
Taillefer, who sung well and loud, Came mounted on a charger proud; Before the duke the minstrel sprang, And the Song of Roland sang.
Brut of Wace (translated).
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894