The 8-cent San Juan postage stamp was first placed on sale at San Juan, Puerto Rico, on September 12, 1971.
Issued to recognize the 450th anniversary of San Juan, Puerto Rico, the stamp depicts a sentry box from Castillo de San Felipe del Morro. San Juan was founded in 1519, and construction on the fortress began in 1539 to protect the city's seacoast.
The stamp was designed by Walter Brooks and issued in sheets of fifty, with an initial printing of 130 million.
Postal Bulletin (August 12, 1971).
National Park Service. "El Morro." http://www.nps.gov/archive/saju/morro.html.