Panama Canal Zone
The Panama Canal Zone () was an unincorporated territory of the United States from 1903 to 1979, centered on the Panama Canal and surrounded by the Republic of Panama. The zone consisted of the canal and an area generally extending on each side of the centerline, excluding Panama City and Colón, which otherwise would have been partly within the limits of the Zone. Its border spanned three of Panama's provinces. When reservoirs were created to assure a steady supply of water for the locks, those lakes were included within the Zone.
Postage stamps and postal history of the Canal Zone
The Canal Zone was a strip of territory long and wide across the Isthmus of Panama, and was ceded to the United States for the purpose of constructing and operating the canal which connected the Atlantic and Pacific Oceans. Upon the establishment of the Canal Zone in 1903, seventeen Post Offices had also been established and were operated by the U.S. Government. The Canal Zone and its post offices, with the main distributing office in Cristobal, operated as an independent government agency under the direct authority of the President of the United States. In the towns where there were railroad stations, the station agents of the Panama Railroad functioned as postmasters. Along with ships and freight, domestic mail and mail from around the world moved through the canal. The Canal Zone Post Office began operating and issued its first postage stamps on June 24, 1904. Initially these were the current stamps of Panama or (less often) the U.S., overprinted with 'CANAL ZONE' in various styles. Philatelists have identified over 100 varieties, some of them quite rare (and counterfeited).