Numerical digit
From India, the thriving trade between Islamic sultans and Africa carried the concept to Cairo. Arabic mathematicians extended the system to include decimal fractions, and Muḥammad ibn Mūsā al-Ḵwārizmī wrote an important work about it in the 9th  century. The modern Arabic numerals were introduced to Europe with the translation of this work in the 12th century in Spain and Leonardo of Pisa's "Liber Abaci" of 1201. In Europe, the complete Indian system with the zero was derived from the Arabs in the 12th century.
Arabs in Europe
The Iberian Peninsula was mapped as "Al-Andalus" by the new Muslim invaders. The Arabs, as well as the overall Muslim populations (a mix of Berbers and Arabs) of Al-Andalus and North Africa, were referred to as "Moors". Spain enjoyed a golden era of Islamic culture, accompanied by a golden age of Sephardic Jewish culture. This era spawned great Arabic polymaths and intellectuals such as Averroes and Albucasis. The Islamic rule in Spain also saw the birth of the Aljamiado alphabet, an Arabic alphabet for the Spanish language. In the 15th century, the Muslims were defeated by the Christian armies in a historical process called Reconquista (meaning reconquest in Spanish and Portuguese), which led the Christian monarchs to regain control over the Hiberian peninsula. Much of the architecture that was concocted from this era remains intact in Spain and functions as famous tourist destinations since the Catholic monarchs decided to use them rather than destroy them.