The origins of the Cossacks are disputed. Originally, the term referred to semi-independent Tatar groups ("qazaq" or "free men") who inhabited the "Wild Fields", or steppes, north of the Black Sea near the Dnieper River. By the end of the 15th century, the term was also applied to peasants who had fled to the devastated regions along the Dnieper and Don Rivers, where they established their self-governing communities. Until at least the 1630s, these Cossack groups remained ethnically and religiously open to virtually anybody, although the Slavic element predominated. There were several major Cossack hosts in the 16th century: near the Dnieper, Don, Volga and Ural Rivers; the Greben Cossacks in Caucasia; and the Zaporozhian Cossacks, mainly west of the Dnieper.