Infante Peter had led minor raids into Granadine territory in 1316 and 1317 [2] and an agreement had been reached with the nobility of Castile in the Cortes held at Medina del Campo in 1318 for a new expedition to begin in the late spring of 1319.

This expedition was to be a large one, blessed by Pope John XXII who authorized it as a crusade and conceded the rebate to the crown of some of the Church tithes in order to finance it.

The large Castilian army encamped in the Vega de Granada [4] and, after looting the immediate area, resolved to return to Castile satisfied with the collected booty.

A large force of elite Moorish cavalry, the "Volunteers of the Faith", led by Uthman ibn Abi al-Ula, exited from Granada and started harassing the retreating Castilians of infante John.

These minor attacks turned into a general assault when the Granadines realized the Castilians were losing their cohesion during their retreat and were unable to fight back effectively.

At this point the vanguard thought only of flight and to reach the Castilian border; in their panic, many men drowned while attempting to cross the river Genil in full armour.