Martyrs' Day is a Panamanian Day of National Mourning which commemorates the January 9, 1964 riots over sovereignty of the Panama Canal Zone. The riot started after a Panamanian flag was torn and Panamanian students were killed during a conflict with Canal Zone Police officers and Canal Zone residents.
U.S. Army units became involved in suppressing the violence after Canal Zone police were overwhelmed, and after three days of fighting, about 21 Panamanians and four U.S. soldiers were killed. The incident is considered to be a significant factor in the U.S. decision to transfer control of the Canal Zone to Panama through the 1977 Torrijos–Carter Treaties.
After Panama gained independence from Colombia in 1903, with the assistance of the U.S., there was resentment amongst some Panamanians as a result of the Hay–Bunau-Varilla Treaty, which ceded control of the Panama Canal Zone to the U.S. "in perpetuity" in exchange for a 10 million dollar initial payment and yearly 250 thousand dollar payments thereafter. In addition, the United States Government purchased title to all the lands in the Canal Zone from the private owners. The Canal Zone, primarily consisting of the Panama Canal, was a strip of land running from the Pacific Ocean to the Caribbean and had its own police, schools, ports and post offices. The Canal Zone became U.S. territory (de facto if not de jure).
In January 1963, U.S President John F. Kennedy agreed to fly Panama's flag alongside the U.S. flag at all non-military sites in the Canal Zone where the U.S. flag was flown. However, Kennedy was assassinated before his orders were carried out. One month after Kennedy's death, Panama Canal Zone Governor Robert J. Fleming, Jr. issued a decree limiting Kennedy's order. The U.S. flag would no longer be flown outside Canal Zone schools, police stations, post offices or other civilian locations where it had been flown, but Panama's flag would not be flown either. The governor's order infuriated many Zonians, who interpreted it as a U.S. renunciation of sovereignty over the Canal Zone.