In 194, however, while Cao Cao was away on a campaign against Tao Qian in Xu Province (徐州; covering present-day northern Jiangsu), Chen Gong defected to a rival warlord, Lü Bu, along with his colleague, Zhang Miao. With the assistance of the two defectors, Lü Bu quickly took over most of Yan Province. Cao Cao hastily returned and laid siege on Lü Bu in Puyang (). After more than hundred days of stalemate, a famine forced Lü Bu to give up his position and seek refuge under Liu Bei in Xiapi (下邳; present-day Pizhou, Jiangsu), capital of Xu Province.