The nuclei of the Great Moravian settlement structure were well-defended fortified settlements built by the local Slavs both on elevated positions and lowland areas like marshes and river islands. Most Great Moravian castles were rather large hill forts, fortified by wooden palisades, stone walls and in some cases, moats. The typical Great Moravian ramparts combined an outer drystone wall with an internal timber structure filled with earth. The fortifications usually formed several contiguous enclosures, with the elite buildings concentrated in the centre and crafts in the outer enclosures. Most buildings were made of timber, but ecclesiastical buildings and residential dwellings were made of stone. In many cases, prehistoric fortifications were also integrated. The Great Moravian towns, especially in Moravia, but also in the lowlands of Slovakia, were frequently far from the place where the stone was mined and material was transported dozens of kilometres.