Battle of Żownin The Battle of Żownin ( or Żołnin ) was an engagement between the Polish - Lithuanian Commonwealth forces under hetman Mikołaj Potocki , supported by the forces under magnate Jeremi Wiśniowiecki , and Cossacks commanded by Yakiv Ostranin ( Jakub Ostrzanin ) and Dmytro Hunia during the Ostrzanin Uprising in Summer 1638 . After a prolonged siege , the Cossacks were defeated and surrendered to the Commonwealth forces . Background . The unrest in Ukraine among Cossacks remained high following the defeat of the Pawluk Uprising in 1637 . After the uprising , the Sejm passed a law setting the number of registered Cossacks at 6 , 000 , and declaring all others peasants . This led to a new mobilization of Cossacks , this time led by Yakiv Ostranin , Dmytro Hunia and Skidan . Battle . After several smaller battles , the Commonwealth forces under Prince Jeremi Wiśniowiecki caught up with the Cossack force under Ostranin and Hunia near Żownin on the morning of 13 June . Wiśniowiecki decided to attack the Cossacks as soon as possible to prevent them from building a tabor fortification . He was soon reinforced by most of the Commonwealth army under regimentarz Stanisław Potocki . The Poles deployed their infantry and artillery in the center , and the cavalry on the flanks , with the right flank under Wiśniowiecki , and the left under Potocki . Wiśniowiecki was able to break through the Cossack defenses , but Potocki fared less well , and Wiśniowiecki found himself surrounded after breaching the Cossack fortifications . After three charges , which he led personally , and in one which he lost a horse , Wiśniowiecki succeeded in breaking back through the Cossack fortifications and returning to the Polish camp that evening . Nonetheless , Wiśniowiecki ' s charge was enough for some Cossacks , including Ostranin , to abandon the camp and run away ; the Cossacks would elect a new leader , Dmytro Hunia . On the morning on the next day , Wiśniowiecki led an infantry assault . The Cossacks , expecting reinforcement , had begun negotiations , which , however , broke down quickly . In the meantime , Cossack reinforcements under Skidan fared less well , losing some skirmishes . In the end , only a part of them broke through to the Cossack camp , and Skidan himself would be captured during the assault on 16 June . The siege dragged on , as the Cossack fort was well built , and the besieging forces failed to prevent small parties of reinforcements from relieving the Cossacks . The Polish forces were also lacking in infantry and ammunition for the artillery . Before Polish reinforcements under Hetman Mikołaj Potocki arrived around 21 June , the Cossacks under Hunia succeeded in building a bridge in the night and moving the entire camp to a new location nearby . Potocki arrived soon after the Cossacks finished their relocation , on the 22nd . It would be a week before the Polish forces were reinforced by the much - needed artillery . Despite the artillery support , a new assault on 10 July failed to take the camp . The Commonwealth forces decided to wait for the Cossacks to run out of supplies . In the meantime , on the night of 22 to 23 July , a few dozen Cossacks managed to sneak into the Polish camp , kill a number of artillery personnel , and almost succeed in wrecking the entire artillery section . Meanwhile , another Cossack leader , Filonienko , attempted to relieve the camp , bringing much needed supplies . On 4 August , two battles took place : another assault on the camp , and a battle against the Cossack reinforcements . To bypass the Polish cordon , Filonenko used river boats ( " czajki " ) to approach the camp . Hunia attempted to aid Filonienko with a counterattack outside the camp , and the forces clashed outside the walls of the Cossack camp in a battle that lasted the entire day . Eventually Filonienko made it to the camp , but with only a few hundred troops , and without any supplies . That night , Hunia escaped from the camp , seeking asylum in Muscovy . Aftermath . Abandoned by their leader , the Cossacks entered negotiations on 7 August and surrendered soon afterward .