Key Christian centers in Eastern Europe and across the Mediterranean regions helped promote aspects of Byzantine spirituality, culture, and art in the regions of the Danube River, such as the principalities of Wallachia and Moldavia. The monasteries on Mount Athos and the monastery of Saint Catherine at Mount Sinai served as important sites that benefited from far-reaching support, including assistance from the Moldavian and Wallachian rulers. Drawing on textual sources and material evidence, this chapter explores the connections between Mount Athos, Mount Sinai, and the Danubian lands during the fifteenth and sixteenth centuries, the manifold implications of patronage, and the impact of these holy sites in the local formulations of piety and ruling ideologies.