The Slavic-Celtic connections have more than thousand-year history. These constant interactions couldn’t but have a religious influence on kindred Slavic tribes. Especially because not the ethnic accessory, but the belief that had the ancient Indo-European roots was important for Celts. The druids exposed to persecutions and destruction by Romans during the pagan period, were not less severely expelled and destroyed by Christians except for that part of this once powerful order which has accepted Christianity. So Slavs-pagans were their natural allies in the military and in spiritual aspect, and druids, as the carriers of the higher knowledge, higher wisdom could give a basis for development of Slavic priestly caste which had a base for influence on military estate.

The Celts have found in Slavs not only natural allies, but also that most ancient Indo-European substratum which was in due time a basis of druidism, and has helped the Slavic priests and Celtic druids to understand each other. Especially it concerns the western Slavs, exposed to celtization first among Slavic tribes and northern Russia, which was their cultural and ethnic successor. At the western Slavs as it will be visible from the further comparison of sources, priest stood above prince, And this system of mutual relations of two branches of authority has organically passed to Russian north.