The Battle of Monterrey was the US Army's first major encounter with urban warfare. It occurred in September 1846 when the US Army under Zachary Taylor invaded the town. The US Army had no prior training in urban warfare and the Mexican defenders hid on rooftops, shot through loopholes, and stationed cannons in the middle of the city's streets. The houses at Monterrey were made of thick adobe, with strong double doors and few windows. The rooftops were lined with a two-foot-tall wall that acted as a parapet for the defending soldiers. Each home was a fort unto itself.