At the end of the 3rd century, the emperor Diocletian made a new territorial distribution of the Roman Empire: from that moment on it will be divided in two demarcations, the Eastern and the Western, and each one of them in dioceses and provinces. Parting from this territorial division, the Church began configurating and distributing itself throughout the whole Empire; also here, in the Hispania Tarraconensis, where the province capital will be Tarragona (Tarraco) and there will be certain dioceses -episcopal sees- that will emerge later, like Barcino in the 4th century and Egara in the 5th century.

This territorial organization -with few changes- was maintained until the 15th of June of 2004, when the pope John Paul II erected two new dioceses: Sant Feliu de Llobregat and Terrassa, converting Barcelona in metropolitan see and these two in their suffragans.