This project explores the significance of the Caucasus and the Danube as frontiers and as contact zones of Byzantium and Orthodox Christianity from Late Antiquity to the Early Ottoman period, as it impacts Central and Eastern Europe, on the one hand, or the Middle East, including the Christian Orient, and the Eurasian Steppes, on the other. Processes of exchange as well as conflict are highlighted in their short- and long-term dynamics on the basis of written sources and material culture and examined from the perspectives of political, religious, economic and environmental history.