Mid-century of the 4th century Barcelona already has a Christian community well organised and structured, with a cathedral and its baptistery. After a period of persecutions, the emperor Constantine tolerated Christianism (313), and eventually Theodosius made it the official religion of the Empire (380). From that moment on, the bishop figure grew in importance, in the sense that exercised true governmental functions.
In 450 was born a new diocese in Barcelona’s territory: Egara (Terrassa), formed by the territories of the current Vallès and, perhaps, part of Baix Llobregat. Its episcopal ensemble has been preserved largely and it is one of the best examples of architecture of the 5th and 6th century in Western Mediterranean.
When the Western Roman Empire fell (476), Barcelona became part of the Visigoth kingdom, from which was the capital twice, in the 5th and 6th century. As the Visigoths professed Arianism (a Christianism variant that was not in communion with Rome), a new cathedral was erected where the current basilica of SS. Justus and Pastor, Martyrs is today.
Conquests and borders
From the 8th century Barcelona, we have very little information: once it was conquered by Arabs it became a part of the Al-Andalus, and it seems that at least part of the cathedral was transformed into a mosque. In 801, the city capitulated to Louis the Pious, Charlemagne’s son, who then incorporated the city to the Carolingian Empire, thus ending the Muslim dominion.
Throughout the 9th century, Barcelona’s diocese was a border territory, in direct contact with Islam. Between the 9th and 10th centuries, the counts conquered slowly the lands beyond the Llobregat, forming the Penedès March.
It was a time of economic and cultural exchanges, but also tough razzias, like the one led by AlMansur in 985, that according to the chronicles razed the city. Meanwhile, the counts would stop depending on the French king, who was not able to defend these far-away-from-the-Carolingianpower territories.