In 1670 Razin, while ostensibly on his way to report at the Cossack headquarters on the Don, openly rebelled against the government, capturing Cherkassk and Tsaritsyn. After capturing Tsaritsyn, Razin sailed up the Volga with his army of almost 7,000 men. The men traveled toward Cherny Yar, a government stronghold between Tsaritsyn and Astrakhan. Razin and his men swiftly took Cherny Yar when the Cherny Yar streltsy rose up against their officers and joined the Cossack cause in June 1670. On June 24 he reached the city of Astrakhan. Astrakhan, Moscow's wealthy "window on the East," occupied a strategically important location at the mouth of the Volga River on the shore of the Caspian Sea. Razin plundered the city despite its location on a strongly fortified island and the stone walls and brass cannons that surrounded the central citadel. After massacring all who opposed him (including two Princes Prozorovsky) and giving the rich bazaars of the city over to pillage, he converted Astrakhan into a Cossack republic. In 1671, Stepan and his brother Frol Razin were captured at Kagalnik fortress (Кагальницкий городок) by Cossack elders. Stepan was then executed in Moscow.