[1] The world heritage site consists of several historic defensive structures built by the Spanish Empire between the 16th and 20th centuries to defend the strategically located colonial city of San Juan and its bay from foreign attacks.

[4] It was Puerto Rico's first inscription and one of the two world heritage sites under United States jurisdiction proclaimed during that session along with the Great Smoky Mountains National Park.

[8] Historic sites in the United States that are neither part of nor owned by the National Park Service (NPS) are often required to be given this special designation by the federal government before they can be officially nominated into the UNESCO World Heritage Tentative List.

Media reports often conflate this narrowly tailored UNESCO listing with the much broader area covered by the Old San Juan Historic District.

[14] That year, Old San Juan became a National Historic Landmark District, therefore meeting the designation required before it can be nominated to the World Heritage Tentative List.