The El Cid who fought at Bairén was not yet the burnished legend of song and film. He was a hard, brilliant, deeply pragmatic warlord. Three years earlier, on the 17th of June 1094, he had taken the wealthy Muslim Taifa of Valencia and made himself the ruler of his own Principality of Valencia, governing a Mediterranean city-state that answered to no king. That independence made him a magnet for enemies, and the most formidable were the Almoravids, the North African dynasty sweeping up through al-Andalus, determined to roll back Christian gains and topple the upstart lord of Valencia.

El Cid did not face them alone. Later in 1094, at Burriana, he cemented an alliance with Peter I of Aragon, both men fixed on the same goal of meeting the Almoravids in open battle. The immediate task was logistical. In December 1096, El Cid set out with Aragonese troops to carry weapons, ammunition, and supplies to the castle of Sierra de Benicadell, a stronghold he had seized back in October 1091 to control the interior route into Valencia from the south. Through January 1097 the Almoravid commander Muhammad ibn Tashfin shadowed them from Xàtiva, harassing the column, but the allies reached the castle and resupplied it as planned.

Their work done, El Cid and the king turned north, and it was on that march that the trap sprang shut. They had camped at Bairén, a few kilometers north of Gandía, when the Almoravids seized the high ground of Mondúver and brought their fleet in against the shore. It was a well-laid ambush, exploiting terrain and sea together to pin the Christians in a killing crossfire. Arrows came from above and from the water at once. For an army caught in the open, with the enemy holding both the heights and the coast, the odds were grim, and the men knew it.

El Cid's answer was not defense but attack. One morning he gathered his troops and, in the old phrase, harangued them, ordering a single frontal charge straight into the Almoravid center. There would be no maneuvering out of the trap; they would break through it or die in it. By midday the assault was in full swing. The Almoravids, stunned by the sheer desperate ferocity of men who had every reason to fight to the last, could not hold. Their center buckled, then shattered, and the disciplined army that had set the ambush dissolved into a fleeing crowd.

The rout was terrible. As the Almoravid soldiers fled in disarray, a river cut across their line of escape, and many drowned in its current. Others waded into the sea, trying to reach the ships of the armada that had brought them, and drowned there too, weighed down and panicked within sight of safety. These were men who had held the high ground a few hours before, now dying in water rather than by the sword. El Cid's forces looted the abandoned camp and gathered rich spoils, then continued their march unmolested to Valencia. The lord of the city had escaped the vise, and kept his principality a while longer.