The Chortomlyk Sich was built at the mouth of the Chortomlyk River in 1652. In 1667 the Truce of Andrusovo made the Sich a condominium ruled jointly by Russia and the Polish–Lithuanian Commonwealth. During the reign of Peter the Great, Cossacks were used for the construction of canals and fortification lines in northern Russia. An estimated 20–30 thousands were sent each year. Hard labour led to a high mortality rate among builders, and only an estimated 40% of Cossacks returned home. After the Battle of Poltava in 1709, the Chortomlyk Sich (sometimes referred to as the "Old Sich" (Stara Sich)) was destroyed and Baturyn, the capital of Hetman Ivan Mazepa, was razed. Another sich was built at the mouth of the Kamianets river but was destroyed in 1711 by the Russian government. The Cossacks then fled to the Crimean Khanate to avoid persecution and founded the Oleshky Sich in 1711 (today the city of Oleshky). In 1734, they were allowed to return to the Russian Empire. Suffering from discrimination in the Khanate, Cossacks accepted the offer to return and built another Sich in close proximity to the former Chortomlyk Sich (referred to as the "New Sich"). The population in steppe region numbered around 52,000 in the year 1768. Fear of the independence of the Sich resulted in the Russian administration abolishing the Hetmanate in 1764. The Cossack officer class was incorporated into the Imperial Russian nobility (Dvoryanstvo). The rank and file Cossacks, however, including a substantial portion of the old Zaporozhians, were reduced to peasant status. Tension rose after the Treaty of Küçük Kaynarca, when the need for a southern frontier ended after the annexation of the Crimea. The colonisation of Novorossiya (New Russia) with Serbian and Romanians sponsored by Russia created further conflict. After the end of the war between Russia and the Ottoman Empire for possession of the Black Sea and Crimean steppes, Russia no longer needed the Zaporozhian Cossacks for protection of the border region. Russia finally destroyed the Zaporozhian Sich through military force in 1775. Destruction and aftermath In May 1775, Russian General Peter Tekeli received orders to occupy and destroy the Zaporozhian Sich from Grigory Potemkin, who had been formally admitted into Cossackdom a few years earlier. Potemkin was given direct orders from Catherine the Great. On 5 June 1775, Tekeli surrounded the Sich with artillery and infantry. He postponed the assault and even allowed