Isthmus of Perekop
Over the course of the 16th century, the outer border of the "Wild Steppes" was near the city of Ryazan, outside the Oka River. The main path for the invading forces to Moscow was the Muravsky Trail, running from the Crimean Isthmus of Perekop, between the basins of the Dnieper and Seversky Donets rivers, and finally up to Tula. The Tatars would turn back only after extensive looting and kidnapping, the Tartars usually managed to penetrate 100–200 kilometers into Russian territory. Captives were subsequently sent to the Crimean city of Caffa to be sold into slavery. As a result, the Russian population in the border regions suffered heavily.