Ringing North and South America, bisecting the Atlantic and Pacific Oceans, stood the feared Perimeter Security Platforms. Spaced approximately 200 miles apart, these platforms resemble oil-rigs from hell. Their purpose: destroy anything attempting to enter or escape Apocalypse's empire.

The Great Sea Wall of the Lord Apocalypse was capable of repulsing ten thousand Sentinels. It was responsible for the defense of North America from immediate attack from Europe and nearly any renegade efforts of the Human High Council. During the last hour of Apocalypse's reign, the worst fears of the Human High Council were realized as Apocalypse's defense grid was no longer limited to defense.

It was infiltrated by Weapon X and Jean Grey who took out the control center for a small sector, allowing passage for the Great Airlift. With the Sentinel Evacuation a success, the High Council was poised for a nuclear strike. This effort was almost thwarted by the combined efforts of the Sea Wall defenses and a band of Altered Humans, but was averted when Gateway provided a teleportional rift large enough for an armada of ships to pass through and reach North America.