Tariq ibn Ziyad, commander of the Berber garrison at Tangiers, crossed the strait and landed at the Rock of Calpe -- the future Gibraltar, whose name derives from the Arabic Jebel Tariq, the Rock of Tariq. A legend recorded by al-Idrisi claims he burned his boats after landing to prevent desertion, though no contemporary source confirms this. The crossing was not an isolated attack but the culmination of raids that had harassed the southern Iberian coast since the conquest of Tangiers around 705-706. Tariq is said to have landed with 7,000 horsemen and requested 5,000 more from his superior, Musa ibn Nusayr. Modern estimates suggest the actual force may have been far smaller -- perhaps as few as 2,000 fighters -- but even this was enough to exploit the Visigothic kingdom's fatal weakness: it was not organized for war.

King Roderic ruled a fractured realm. He had come to power under disputed circumstances after the death or assassination of his predecessor Wittiza, and a rival named Achila II controlled the northeast. According to al-Maqqari, Roderic was fighting the Basques in the north when word came that he needed to march south. The Mozarabic Chronicle, the nearest source in time to the events, describes the kingdom as consumed by intestino furore -- internal frenzy. Some of Roderic's own nobles had accompanied the royal army not out of loyalty but, as the chronicler wrote, "in rivalry, deceitfully, and out of ambition to rule." Whether they planned to betray him on the field or simply seized the opportunity when it arose, the result was the same.

The battle itself, fought over perhaps a week of skirmishes near the marshy plain between the rivers Barbate and Guadalete, ended in catastrophe for the Visigoths. A cavalry wing that had secretly pledged to rebel against Roderic stood aside at the critical moment, opening a gap in the Christian lines. Tariq's cavalry -- the mujaffafa, armored in light mail and identifiable by turbans wound over metal caps -- charged through the breach into the Visigothic infantry. The king died in the final hours of battle. Visigothic losses were devastating, and the Muslim army suffered roughly 3,000 casualties, perhaps a quarter of its strength. The treachery benefited no one on the losing side; Roderic's rivals were largely slaughtered alongside him. Within a decade, nearly the entire Iberian Peninsula lay under Muslim control, save the tiny Kingdom of Asturias in the far north.

The battle's significance is inversely proportional to the reliability of its sources. The primary account, the Mozarabic Chronicle written shortly after 754, provides sparse detail. Later Arabic sources, beginning with Ibn Abd al-Hakam writing around 860, offer richer narratives but increasingly contradict each other. Historians Roger Collins and E. A. Thompson rely heavily on the Mozarabic Chronicle and treat the Arabic accounts with skepticism. The exact location remains uncertain -- candidates include the Guadalete river valley, the dried Lake La Janda, the Barbate river, and even the banks of the Guadarranque, which one scholar suggests derives from Wad al-Rinq, meaning Roderic's river. What is certain is the outcome: the Visigothic capital of Toledo fell shortly after, and eight centuries of al-Andalus had begun.