On May 4, 1648, near Kamianyi Zaton, Mykhailo Krychevsky's 3,500 registered Cossacks mutinied, killing all the officers (Krychevsky himself was taken prisoner and would join Khmelnytsky's army). Cossacks who stayed loyal to the Crown, such as Ivan Barabash, were cut down, as well as the German dragoons in their midst. Rebellious Cossacks arrived at the battlefield on May 13. The next day, Stefan Potocki saw his already undermanned force dwindle to 1,000 men, when the 1,200 registered Cossacks and some dragoons who arrived with Stefan also joined the uprising. Polkovnyk Ivan Hanzha is recognized as being instrumental in swaying his fellow registered Cossacks into taking Khmelnytsky's side. This created a gap in the Polish defense which the Cossacks attacked, supported by Tatars, but the attack was repulsed. At this point, Khmelnytsky's army swelled to more than 11,000. Despite the overwhelming numerical superiority, gaining Polish ramparts was not an easy task, especially in the absence of heavy artillery on the side of the Cossacks. Therefore, the Tatars and Cossacks decided to capture the Polish camp by guile. On the same day Tugay Bey proposed Poles negotiations.