During World War II, construction of military bases and the presence of larger numbers of U.S. military and civilian personnel brought about unprecedented levels of prosperity to the city. Panamanians had limited access, or no access at all, to many areas in the Canal Zone neighboring the Panama city metropolitan area. Some of these areas were military bases accessible only to United States personnel. Some tensions arose between the people of Panama and the U.S. citizens living in the Panama Canal Zone. This erupted in the 9 January 1964 events, known as Martyrs' Day.