The culture of Belarus is the product of a millennium of development under the impact of a number of diverse factors. These include the physical environment; the ethnographic background of Belarusians (the merger of Slavic newcomers with Baltic natives); the paganism of the early settlers and their hosts; Byzantine Christianity as a link to the Orthodox religion and its literary tradition; the country's lack of natural borders; the flow of rivers toward both the Black Sea and the Baltic Sea; and the variety of religions in the region (Catholicism, Orthodoxy, Judaism, and Islam).