Christianity spread very quickly and well in what is now Bulgaria, and we draw our knowledge primarily from the monuments that supplement the sparse written sources. Nevertheless, this area also had supra-regional importance as the foreland of the capital Con-stantinople. It also shows influences from the Middle East, especially on the Black Sea coast. End of the 4th century the migration of mainly Germanic groups into the Roman Empire began, although the integration of these was made more difficult by the fact that the immigrants often quickly adopted the Christian faith, but in the form of so-called Arianism. But not only the onslaught of various peoples, but especially the internal political and economic difficulties of the Roman Empire led to the collapse of the Limes in the 6th century, i. e. in our case the border protection on the Danube and finally the immigration of the Slavs