The Zaporozhian Sich (; ; , Zaporoz'ka Sich) was a semi-autonomous Cossacks' polity in the 16th–18th centuries, centred in the region around today's Kakhovka Reservoir spanning across the lower Dnieper river. In different periods, the area was under the sovereignty of the Polish-Lithuanian Commonwealth, the Ottoman Empire, the Tsardom of Russia, and the Russian Empire. In 1775, shortly after Russia annexed the territories ceded to it by the Ottoman Empire under the Treaty of Küçük Kaynarca (1774), the Sich was disbanded and incorporated into the Russian province of Novorossiya.