Christianity was established in the region by the Romans, and saw the establishment of monasteries and churches in the high regions. The Frankish expansion of the Carolingian Empire and the Bavarian expansion in the eastern Alps introduced feudalism and the building of castles to support the growing number of dukedoms and kingdoms. Castello del Buonconsiglio in Trento, Italy, still has intricate frescoes, excellent examples of Gothic art, in a tower room. In Switzerland, Château de Chillon is preserved as an example of medieval architecture.