Cao Cao returned to his base in Xu (許; present-day Xuchang, Henan) sometime between 20 August and 18 September 198. When Xun Yu asked Cao Cao how he knew he would definitely defeat Zhang Xiu when he wrote the letter to Xun Yu earlier during the battle, Cao Cao replied: "The enemy wanted to prevent me and my men from retreating. In doing so, they were forcing us to fight for our lives. That was when I knew we would definitely win."