On August 13, with American commanders unaware that a ceasefire had already been signed between Spain and the U.S. on the previous day, American forces captured the city of Manila from the Spanish in the Battle of Manila. The battle started when Dewey's ships bombarded Fort San Antonio Abad, a decrepit structure on the southern outskirts of Manila, and the virtually impregnable walls of Intramuros. In accordance with the plan, the Spanish forces withdrew while U.S. forces advanced. Once a sufficient show of battle had been made, Dewey hoisted the signal "D.W.H.B." (meaning "Do you surrender?), whereupon the Spanish hoisted a white flag and Manila was formally surrendered to U.S. forces.