I believe The Battle of Guadalete was one of the most decisive battles in the world. It was in Islamic Spain that had enlightened Europe and brought it out of the dark ages to usher in the renaissance. Many of their cultural and intellectual influences still live with us today.
Battle of Guadalete (July 19, 711)
This battle took place close to the Guadalete River near the southern coast of the Iberian peninsula, between Muslim and Visigothic forces. An Arab and Amazigh (Berber) Muslim army of 7,000-10,000 soldiers crossed to Spain -- the land of the Vandals or Andalus as they called it -- from North Africa. The Amazighs (Berbers) possibly received the help of the governor of Ceuta, Count Julian. He confirmed that the peninsula offered numerous riches. The forces landed near a large mountain. It was later named Gibraltar (jabal Tariq, or Tariqs mountain) in homage to the army commander, Tariq ibn Ziyad.
According to one account, Tariq burned the ships used for the crossing and stirred his troops with the words: O People! There is nowhere to run away! The sea is behind you, and the enemy is before you. I swear to God, you have only sincerity and patience.
Roderic was a Visigothic nobleman recently chosen as king. He had been fighting Basques in the north. Upon hearing of the new threat in the south, he rushed to meet the Muslims. His army is said to have been nearly 10 times larger than the Muslim forces.
With the routing of the Visigothic army -- including many prominent nobles -- the Muslim forces continued northward unhindered. They established garrisons in major cities and conquered many regions. Within a few years, virtually the entire peninsula came under Muslim rule.
The Visigothic kingdom came to an abrupt end. However, a local Asturian strong man named Pelayo fled to the extreme north beyond the reach of Muslim armies. (See below.) There, he founded the Kingdom of Asturias. In subsequent centuries, Asturias was regarded as the origin point for the Reconquista.