In 710 RODRIGO was elected King of Visigothic Spain, against the votes of his opponents who called in Arab troops under TARIQ BIN ZIYAD from nearby North Africa. Tariq and his forces crossed the Straits of Gibraltar and landed at Gibraltar (in Arabic : Jebel et-Tariq or the Mountain of Tariq) and defeated Roderic's Visigothic forces in 711; Roderic himself fell in battle.
In 712, Tariq's superior, MUSA BIN NUSAYR, crossed into Spain with even larger forces. Within a few years, Muslim rule over the Iberian peninsula was established. On the peninsula there were only few areas resisting Muslimic rule, TODMIR on the eastern coast, and the mountainous region of ASTURIAS, where Visigothic nobleman PELAYO defeated a Muslim force in 717 (BATTLE OF COVADONGA).
What turned out to become the Islamic conquest of Spain seems, by many contemporaries, both Visigoths and Muslims, regarded merely a raid, a temporary undertaking; as late as 717 Caliph 'Umar ordered his Muslim subjects to evacuate the Iberian peninsula. H. Kennedy (p.10) points out that a faction of Visigothic nobility opposed to King Roderick might have welcomed a defeat inflicted on him by outside invaders.
The Muslim conquest of North Africa and Spain was, to the larger extent, accomplished by frontier peoples recently converted to Islam. As they were not paid for their efforts, their reward would come out of the partition of confiscated, conquered lands. So soon after Tariq's victory over Roderic, Muslims - both Berbers and Arabs - began to settle on the peninsula, and the Muslim community established there proved to strong to uproot by an evacuation order coming from Damascus.
The Muslim conquest of Spain is part of the Muslim expansion over western north Africa; this process lacked a central control - neither Damascus nor Egypt or Kairouan were able to establish more than temporary control of the situation. While the Muslim Emirs of Spain might have recognized the sovereignty of the UMAYYAD CALIPHATE, local policy was by and large determined by the settlers, although governors of Muslim Spain were appointed in Kairouan. On the fringes, profitable raids continued.
CORDOBA became the administrative center of Muslim rule over the peninsula, soon to become the capital of the UMAYYAD EMIRATE OF CORDOBA. Muslim Spain was urbanized, with flourishing cities such as Granada, Sevilla, Toledo, Zaragoza, Valencia, Badajoz and others, some of which only grew into mahor urban centers under Muslim rule. The Caliphate tolerated religious communities such as JEWS and Christians. Christians living under Muslim rule were called MOZARABS.
Todmir fell before 741. Only Asturias held out.
Spain became the staging area for raids into the Frankish kingdom. In 732, a Saracen raiding party accidentally ran into a Frankish army headed by CHARLES MARTEL, who defeated them in the BATTLE OF POITIERS. Further south, the Saracens occupied SEPTIMANIA and established a bridgehead in FRAXINETUM in the Provence, from which raids were undertaken as far as St. Gallen monastery, located in modern Switzerland.
http://www.zum.de/whkmla/region/spain/arabconquest.html