Thus destroying Energy Cores to disconnect parts of an enemy's base is a possible strategy on certain maps.

Energy Cores can activate the titular Perimeter, an impenetrable barrier that destroys any enemies passing through it.

The Spirits, foreseeing the inevitable destruction of Earth due to the ravages of our time, directed scientific efforts into the discovery of a new plane of existence: the Psychosphere.

The Psychosphere is appropriately named, as the various worlds resemble the thoughts and actions that have occurred upon Earth during its history.

The Spirits then embarked upon the construction of massive floating city-ships called Frames, which could house hundreds of thousands of people for an indefinite period of time.

With the Frames completed, the Spirits sent them forth into the Psychosphere with the intent to lead their people to the Promised Land, leaving Earth behind forever.

The general populace were kept sedate and forced into a ritualistic spiritualism to control their minds, for it was soon discovered that the Psychosphere reacted to negative emotions; causing creatures known as Scourge to erupt out of the very ground and attack the Frames.

[16] A stand-alone expansion pack titled Perimeter: Emperor's Testament was published by 1C Company and first released in Russia in November 6, 2005.

In 2021 the chief creator Andrey KranK Kuzmin released source code to GitHub with an open license GPLv3, excluding game data (models, textures, music).