The Balance Wall of Lights
The Walls of Lights on the Serpent Isle are a connection to the Ethereal Void, and to other places, planes and dimensions, although its exact nature remains a mystery. They were built by the Ophidians so that their highest priests could visit the three Serpents in the Void. They also enable others travel as long as the correct Serpent is used. One, or all of the Blackrock Serpents are needed to actually activate the walls.
There exist three Walls of Light on the Serpent Isle, one for Order, one for Chaos and one for Balance, and they are each different to the other, having their own history, key and light effects.
Wall of Lights - Balancing the Scales
Order[]
The Order Wall of Lights is found in Spinebreaker, and can only be properly used with the Order Blackrock Serpent (it can be opened with the others, too, but walking through it won't work). The Wall is glowing blue and white. The forces of Order used it to leave the Serpent Isle after the War of Imbalance for an unknown place. In Ultima VII Part Two, Batlin wanted to go through it, but since the Soul Prisms were subjected to the energies emanating from it, they exploded, releasing the Banes. The Guardian withdrew his protection from Batlin at that precise moment.
Chaos[]
The Chaos Wall of Lights is found in Skullcrusher, and can only be properly used with the Chaos Blackrock Serpent (it can be opened with the others, too, but walking through it won't work). This wall glows red and yellow. In Ultima VII Part Two, the Avatar used it to fuse the Chaos Serpent back together, returning it to the Void where it belonged to.
Balance[]
The Balance Wall of Lights is found in the Shrine of Balance, and can only be activated with all three of the Blackrock Serpents. This wall glows red, blue, yellow and white. In Ultima VII Part Two, the Avatar used it to return the Great Earth Serpent to the Void, where it belonged.