The Polish-Muscovite War had no sooner been ended by the treaty of Deulino than Chodkiewicz was hastily dispatched southwards to defend the southern frontier against the Turks, who, in the opening phase of the Polish–Ottoman War, defeated Polish forces at Cecora, killing Hetman Żółkiewski. An army of 160,000 Turks and 60,000 Tatars led by Sultan Osman II in person advanced on the Polish frontier. Opposed it were the Commonwealth forces, numbering about 70,000, half of them a Cossack detachment under Cossack hetman Petro Konashevych-Sahaidachny. Chodkiewicz crossed the Dnieper in September 1621, and entrenched himself in the Khotyn Fortress, directly in the path of the Ottoman advance. During the Battle of Chocim Chodkiewcz resisted the sultan's 200-thousand army for a whole month. but the cost of victory was his life. A few days before the siege was raised and the Ottomans decided to open negotiations, the aged Grand Lithuanian Hetman, already suffering from illness since the very start of this campaign, died in the fortress on 24 September 1621.