After the decline of the Roman Empire, Germanic tribes invaded the former empire. Several turned sedentary and created successor-kingdoms to the Romans in various parts of Europe. Iberia was taken over by the Visigoths after 410.
In the Iberian peninsula, as elsewhere, the Empire fell not with a bang but with a whimper. Rather than there being any convenient date for the "fall of the Roman Empire" there was a progressive "de-Romanization" of the Western Roman Empire in Hispania and a weakening of central authority, throughout the 3rd, 4th and 5th centuries. At the same time, there was a process of "Romanization" of the Germanic and Hunnic tribes settled on both sides of the limes (the fortified frontier of the Empire along the Rhine and Danube rivers). The Visigoths, for example, were converted to Arian Christianity around 360, even before they were pushed into imperial territory by the expansion of the Huns. In the winter of 406, taking advantage of the frozen Rhine, the (Germanic) Vandals and Sueves, and the (Sarmatian) Alans invaded the empire in force. Three years later they crossed the Pyrenees into Iberia and divided the Western parts, roughly corresponding to modern Portugal and western Spain as far as Madrid, between them. The Visigoths meanwhile, having sacked Rome two years earlier, arrived in the region in 412 founding the Visigothic kingdom of Toulouse (in the south of modern France) and gradually expanded their influence into the Iberian peninsula at the expense of the Vandals and Alans, who moved on into North Africa without leaving much permanent mark on Hispanic culture. The Visigothic Kingdom shifted its capital to Toledo and reached a high point during the reign of Leovigild.
Importantly, Spain never saw a decline in interest in classical culture to the degree observable in Britain, Gaul, Lombardy and Germany. The Visigoths tended to maintain more of the old Roman institutions, and they had a unique respect for legal codes that resulted in continuous frameworks and historical records for most of the period between 415, when Visigothic rule in Spain began, and 711, when it is traditionally said to end. The proximity of the Visigothic kingdoms to the Mediterranean and the continuity of western Mediterranean trade, though in reduced quantity, supported Visigothic culture. Arian Visigothic nobility kept apart from the local Catholic population. The Visigothic ruling class looked to Constantinople for style and technology while the rivals of Visigothic power and culture were the Catholic bishops— and a brief incursion of Byzantine power in Cordoba.
The period of rule by the Visigothic Kingdom saw the spread of Arianism briefly in Spain. In 587, Reccared, the Visigothic king at Toledo, having been converted to Catholicism put an end to dissension on the question of Arianism and launched a movement in Spain to unify the various religious doctrines that existed in the land. The Council of Lerida in 546 constrained the clergy and extended the power of law over them under the blessings of Rome.
The Visigoths inherited from Late Antiquity a sort of feudal system in Spain, based in the south on the Roman villa system and in the north drawing on their vassals to supply troops in exchange for protection. The bulk of the Visigothic army was composed of slaves, raised from the countryside. The loose council of nobles that advised Spain's Visigothic kings and legitimized their rule was responsible for raising the army, and only upon its consent was the king able to summon soldiers.
The impact of Visigothic rule was not widely felt on society at large, and certainly not compared to the vast bureaucracy of the Roman Empire; they tended to rule as barbarians of a mild sort, uninterested in the events of the nation and economy, working for personal benefit, and little literature remains to us from the period. They did not, until the period of Muslim rule, merge with the Spanish population, preferring to remain separate, and indeed the Visigothic language left only the faintest mark on the modern languages of Iberia. The most visible effect was the depopulation of the cities as they moved to the countryside. Even while the country enjoyed a degree of prosperity when compared to the famines of France and Germany in this period, the Visigoths felt little reason to contribute to the welfare, permanency, and infrastructure of their people and state. This contributed to their downfall, as they could not count on the loyalty of their subjects when the Moors arrived in the 8th century.