Date: c. July 19 A.D. 711
Winner: North African Moors, led by Tarik ibn Aiyad
Loser: Visigoths, King Roderick of the Visigoths
Site: Algeciras near the banks of the Guadalete; Spain
Benson Bobrick's The Caliph's Splendor (Simon & Schuster 2012) describes the conditions that led up to the Battle of Guadelete. The Visigoths were no longer barbarians, but Christian rulers of the part of the Roman Empire covered by the Iberian Peninsula -- Hispania (Spain). They had also wrested part of Gaul/France from Roman control and held onto it until they lost the area to the Frankish King Clovis, founder of the Merovingian Dynasty, who, like the battle itself, falls outside the normal time frame for this site. Bobrick says there were great inequities among the people of Spain. Even among the nobility there were struggles, so when Roderick assumed the throne, he had rivals. Again, according to Bobrick, he raped a noble woman named Florinda, which led her outraged father (Ceuta, Count Julian, according to Andalusi Major Battles) to invite the North African Muslims to help him take the throne from Roderick.
Invited in, the Arab governor, Musa ibn Nasyr, who may never even have considered installing Florinda's father, sent a Berber general named Tarik ibn Ziyad, with a large force, perhaps 12,000 men. Tarik's men met Roderick's near the southernmost part of the peninsula, said to be Algeciras, near the banks of the Guadalete. The Visigoths were terrified by the scimitar-wielding, screaming Berber horsemen and were routed. The North Africans, having entered the Iberian peninsula, pushed on further into the interior. The Visigoths soon lost most of Hispania to the Moors, to be completely regained by the Christians by the time of the late 15th century rulers Ferdinand and Isabella of Christopher Columbus fame.
The Battle of Guadalete is a little beyond the time period usually covered by the Ancient/Classical History site because Muslims were involved and Islam is beyond our scope, by traditional definition. However, this battle marks the end of the period covered by Greg Woolf in his story of the Roman Empire (Rome: An Empire's Story by Greg Woolf; Oxford University Press 2012) who uses the increasingly popular view that late antiquity needs to be studied together with the traditional areas.