Graus was the northernmost Muslim outpost in the valley of the Cinca, a fortified knot on the edge of a young Christian kingdom. Ramiro I had reason to want it. His first attempt, in 1055, likely came in response to shifting fortunes to his west, where Ferdinand I of Leon and Castile was growing dangerously strong after the defeat of Ramiro's kinsman at Atapuerca. That first expedition failed. By 1059 Ferdinand was squeezing tribute, the parias, out of the Muslim taifa of Zaragoza, whose lands included Graus. When Ramiro marched again in the spring of 1063, he was pushing against a target that now had powerful protection, and against a political tangle in which Christian and Muslim rulers were bound together as much by money as by faith.

The strangest feature of Graus is who defended it. The Zaragozans did not stand alone; with them rode 300 Castilian knights under the infante Sancho, called the Strong, sent by a Christian king to protect a Muslim tributary. Frontier war in eleventh-century Iberia rarely divided cleanly along the lines later legend preferred. One source, the generally reliable Historia Roderici, even places a young Rodrigo Diaz de Vivar, the man history would remember as El Cid, at the battle as Sancho's standard-bearer. Historians treat it with caution: the Cid's name is scarce in the records of these years, and his presence here is more likely a later flourish than a fact. The image endures anyway, of Spain's great warrior earning his spurs against the king of Aragon.

The manner of Ramiro's death dissolves the closer you look. One terse chronicle records only that he was killed by the Moors in war near Graus. The scholar Reinhart Dozy argued that Ramiro actually lived four months past the battle, and that neither Sancho nor the Cid took any part. The Arabic historian al-Turtushi tells a sharper tale: a Muslim soldier who spoke the Christians' language infiltrated the Aragonese camp and struck the king down from within. A separate chronicle spins the whole campaign into a story of thwarted love. In its telling, an illegitimate son of the king of Navarre eloped with a young woman betrothed to the Castilian infante Sancho, then fled for protection to Zaragoza and afterward to Aragon, and Sancho marched south to avenge the insult to his marriage plans. Most historians treat this as legend rather than record, but it shows how readily a king's death could be reworked into a tale of passion and honor. These are not merely competing details. They are the fog that settles over a violent moment once the people who lived it are gone, and the poets and partisans take over.

Whatever happened on that day, its consequences were enormous. The death of Aragon's first king left the kingdom reeling and exposed, and word of the catastrophe traveled north across the Pyrenees. Within a year it helped trigger the War of Barbastro, an expedition preached and organized with the backing of the abbey of Cluny and Pope Alexander II, drawing Frankish knights south in what one historian called an Iberian rehearsal for the Crusades. Graus, in that reading, was a Spanish Manzikert, a defeat that summoned foreign armies to a threatened Christian frontier. The town itself would not fall to Aragon until 1083, two decades later, taken at last by Ramiro's son and successor, Sancho Ramirez.