The Zaporozhian Sich or Zaporizhian Sich, also known as the Free lands of the Zaporozhian Host the Lower, was a semi-autonomous polity and proto-state of Zaporozhian Cossacks that existed between the 16th to 18th centuries. For the latter part of that period, it was an autonomous stratocratic state within the Cossack Hetmanate. The lands of Zaporozhian Sich were centred around the Great Meadow region of Ukraine, spanning the lower Dnieper river. In different periods the area came under the sovereignty of the Polish–Lithuanian Commonwealth, the Ottoman Empire, the Tsardom of Russia, and the Russian Empire.
The establishment of Zaporozhian Sich was an important factor in defense of Ukraine and Russia from Crimean-Nogai raids. In c. 1650, its total population consisted of 100,000. In 1657–1687, Zaporizhian Sich was practically independent, possessing its own administration and armed forces consisting of 12,000–20,000 Cossacks. It was reliant on population growth, mainly consisting of Ukrainian refugees from devastated lands.