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As early as the 15th century a few individuals ventured into the proverbial "Wild Fields", the southern frontier regions of Ukraine separating Poland-Lithuania from the Crimean Khanate, which was a naturally rich and fertile region teeming with cattle, wild animals, and fish.
Cossacks were usually organized by Ruthenian boyars or princes of the nobility, especially various Lithuanian starostas.
Merchants, peasants and runaways from the Poland-Lithuania Commonwealth, Moscow state, and modern Moldova and Romania also joined the Cossacks.
The Zaporozhian Cossacks lived on the Pontic-Caspian steppe below the Dnieper Rapids (Ukrainian: za porohamy), also known as the Wild Fields.
They became a well-known group whose numbers increased greatly between the 15th and 17th centuries.
In the 15th century, the Cossack society was described as a loose federation of independent communities, often forming local armies, entirely independent from the neighbouring states (of, for example, Poland, the Grand Duchy of Moscow or the Khanate of Crimea).