The Barrier Cities are the result of Dr. Sid's invention in the movie Final Fantasy: The Spirits Within. The Barriers, powered by bio-etheric ovo-pacs, protect the remaining settlements of the humans on Earth against the Phantoms.
Barrier Cities began as military troop facilities which were built seventeen years after the Leonid Meteor, which carried the Phantoms which fell on the Earth. A total of 130 facilities were built across the world as a base operation for the troops of the United States Military Forces (USMF) in their combat against the Phantom threat. However, due to the development of the Zeus Cannon in 2055, some of the Barrier Cities were not completed until two years later.
During that time, human population began moving into the Barrier Cities, due to the death of plant species which depleted the world's oxygen. Oxygen generators were built within the Barrier Cities, and life outside these settlements became almost impossible.
The only known Barrier Cities are:
- New York Barrier City, which is the base operations of the New York United States Military Force as well as the headquarters of the Council.
- Houston Barrier City, where the Council evacuated themselves after the Phantom attack on New York Barrier City.
- San Francisco Barrier City, which was attacked by Phantoms and where General Hein lost his wife and daughter.
- Chicago Barrier City, Gray Edwards' hometown.
- The Barrier System Theory, developed in 2045, led to the creation of the Barrier City project, aimed at protecting the inhabitants from Phantom attacks through the use of spiritual energy control technology.
- The first experimental small barrier city was completed in 2047.
- In 2048, Barrier City construction commenced for 130 cities and 1200 military facilities around the world.