The Catholic Church in Spain has a long history, starting in the 1st century. It is the largest religion in Spain, with 58.6% of Spaniards identifying as Catholic.
Attempts were made from the late 1st century to the late 3rd century to establish the church in the Iberian peninsula. Paul the Apostle expressed a wish to preach in Spain in the Epistle to the Romans, although most scholars of early Christianity believe Paul did not go on to make an actual journey to Spain. Jerome Murphy-O'Connor holds that Paul did travel to Spain and preach there for up to a few months with little success, most likely because Greek was not widely spoken there. Traditional accounts credit the Apostle James the Great with early preaching of the Christian faith in Spain, but many scholars doubt the historicity of James' presence in Spain.
Canons of the Synod of Elvira (circa 305 AD in Rome) indicate that the church was greatly isolated from the general population even at that time. The situation of the Christians in Iberia improved with the advent of the Edict of Milan in 313 AD, after which Christians were more or less free to openly practice their new religion within the Roman Empire. Over the course of the 4th century, the church built significant footholds particularly around Seville, Cordoba, and Toledo.
Visigoths
As Rome declined, Germanic tribes invaded most of the lands of the former empire. In the years following 410 Spain was taken over by the Visigoths who had been converted to Arian Christianity around 419. The Visigothic Kingdom established their capital in Toledo, their kingdom reaching its high point during the reign of Leovigild. Visigoth rule led to the expansion of Arianism in Spain. In 587, Reccared, the Visigothic king at Toledo, was converted to Catholicism and launched a movement to unify doctrine. The Council of Lerida in 546 constrained the clergy and extended the power of law over them under the blessings of Rome.
Councils of Toledo
About thirty synods, variously counted, were held at Toledo in what would come to be part of Spain. The earliest, directed against Priscillianism, assembled in 400. The "third" synod of 589 marked the epoch-making conversion of King Reccared from Arianism to the Nicene Creed. The "fourth", in 633, probably under the presidency of the noted Isidore of Seville, regulated many matters of discipline and decreed uniformity of liturgy throughout the kingdom. The British Celts of Galicia accepted the Latin rite and stringent measures were adopted against baptized Jews who had relapsed into their former faith. The "twelfth" council in 681 assured to the archbishop of Toledo the primacy of Hispania (present Iberian Peninsula). As nearly one hundred early canons of Toledo found a place in the Decretum Gratiani, they exerted an important influence on the development of ecclesiastical law.
The seventh century is sometimes called, by Spanish historians, the Siglo de Concilios, or "Century of Councils".
Muslim occupation and the reconquest (8th–15th centuries)
By 689, Arabs and Berbers conquered Melilla, and by 709, the then Visigothic Spanish city of Ceuta was taken.By 711, Islam dominated all the north of Africa. The process of islamization of the Berber tribes had begun, though most of the population was still Christian, Jew or polytheist. A raiding party recruited mostly among these newly subjugated, still non-Muslim Berbers and led by convert Tariq ibn-Ziyad was sent to plunder the south of the Visigothic Kingdom of Spain, which faced strong internal tensions and was at the verge of a civil war between the Chindasvintan, Witizan and nobiliary parties. Crossing the Strait of Gibraltar, it won a decisive victory in the summer of 711 when the Visigothic king Roderic was betrayed by the Witizan wings of his army and killed on July 19 at the Battle of Guadalete. Roderic's body was never found, and many rumors about his fate arose, which led to a paralysis on the Visigothic command. Tariq's commander, Musa bin Nusair, quickly crossed with substantial Muslim reinforcements from the Caliphal garrison of North Africa and by 718 the Muslims dominated most of the peninsula. The advance into Europe was stopped by the Franks under Charles Martel at the Battle of Tours in 732.