The first attempt by Ramiro I of Aragon to take Graus, the northernmost Muslim outpost in the valley of the Cinca, had taken place in 1055, probably in response to the defeat of García Sánchez III of Navarre at Atapuerca the year before (1054), which had placed Ferdinand I of León and Castile in a commanding position against Ramiro's western border and the Muslim Taifa of Zaragoza to his south.
His first expedition against Graus had failed, and in 1059 Ferdinand had succeeded in extorting parias (tribute) from Zaragoza.
Ramiro marches on Graus again in the spring of 1063, but this time the Zaragozans have with them three hundred Castilian knights under the infante Sancho the Strong and (possibly) his general Rodrigo Díaz de Vivar, better known as El Cid.
The presence of the Cid at the battle is based on a single source, the generally reliable Historia Roderici, which alleges that he was the alférez of Sancho at the time.
Considering the rarity of the Cid's name in the documents of the early 1060s, this is unlikely.
The circumstances of the actual battle are obscure.
Reinhart Dozy argued that Ramiro survived four months after the battle and that neither the Cid nor Sancho took any part in it.
The Fragmentum historicum ex cartulario Alaonis records only that occisus est a mauris in bello apud Gradus (he [Ramiro] was killed by the Moors in war near Graus), with no mention of the Castilians.
The aforementioned Chronica naierensis contains an account generally, though not universally, regarded as a legend: that Sancho Garcés, an illegitimate son of García Sánchez III of Navarre, eloped with the daughter of García's wife, Stephanie (probably by an earlier marriage), who was the fiancée of the Castilian infante Sancho, and that he sought refuge at the court first of Zaragoza, then later of Aragon.
Sancho, to avenge the disruption of his marriage plans, marched against Ramiro and Zaragoza, and Ramiro died in the encounter near "the place called Graus" (loco qui Gradus dicitur) in 1064 or 1070.
According to the Arabic historian al-Turtūshī, Ramiro (misidentified as "Ibn Rudmīr", the son of Ramiro) was assassinated by a Muslim soldier who spoke the Christians' language and infiltrated the Aragonese camp.
