The Croats were open to Roman art and culture, and first of all to Christianity. First churches were built as royal sanctuaries, and the influence of Roman art was strongest in Dalmatia where the urbanization was thickest and there were the largest number of monuments. Gradually that influence was neglected and certain simplification, alteration of inherited forms, and even creation of original buildings appeared. All of them (a dozen large ones and hundreds of small ones) were built with "roughly cut stone" (natively called – "lomljenac") bounded with thick layer of mortar from outside. Large churches are longitudinal with one or three naves like the St. Saviour at the source of the river Cetina, built in the 9th century. The church has strong semi-circular buttresses that give a feeling of fortification, emphasized by the mighty bell-tower positioned in front of entrance.