The Battle of Guadalete and the Conquest of al-Andalus
Tariq ibn Ziyad, with twelve thousand men, defeated the Visigothic army of King Roderic at the decisive Battle of Guadalete, opening the gates of al-Andalus, which would become a beacon of Islamic civilization in Europe for eight centuries.
Tariq ibn Ziyad crossed the strait that would later bear his name in Rajab 92 AH by leave of Musa ibn Nusayr and landed at the mountain named after him (Jabal Tariq). When word reached him of Roderic advancing with hosts approaching a hundred and forty thousand, he sought reinforcement from Musa, who reinforced him.
The two hosts met on the banks of Wadi Lakka (Guadalete) in the south of al-Andalus for eight days. The wings of Roderic's rivals abandoned their king, the Muslims held firm until the Visigothic army collapsed, and Roderic drowned or was killed in the battle on 28 Ramadan 92 AH (July 711).
After it the cities fell one by one: Cordoba, then the capital Toledo; then Musa ibn Nusayr completed the conquest. In al-Andalus arose a civilization of eight centuries that lit up Europe with knowledge and building, from Cordoba and al-Zahraʾ to Granada and the Alhambra.
Note — differing reports on the date: The well-known view is that the decisive battle was on 28 Ramadan 92 AH after some days of fighting; some sources differ slightly over the numbers and the days.