From Ars Magica
A Gateway is a structure that connects to a portal system that is made by placing a three Stone Bricks in a line (Stone Brick, Chiseled Stone Brick, Stone Brick) then three Stone Bricks on each end with Stone Brick Stairs on the top facing out with the Keystone Receptacle in between the stairs.
A Gateway must be powered with Raw Essence before it will work. A Gateway that does not have enough essence to function will activate, however if insufficient essence is in the gateway to take you all the way to your destination, you will be deposited somewhere in the middle, as far as the essence can take you. A fully charged Gateway will hold 250,000 Essence.
Using the same formula as Recall, this works out to a maximum travel distance of 11,952 blocks.
Gateways are defaulted to the "open" network meaning that anyone activating a gateway, without a keystone in hand, can end up at any "open" gateway. Alternatively, you can assign a gateway a rune address by placing a keystone, with a rune combination, inside the Keystone Receptacle (shift+right click with an 'open hand' to access). To travel to a gateway with an address, right click any Keystone Receptacle with a keystone containing the desired rune address.
In practice, each destination has a specific rune address (each player's house, your mine, the mooshroom island, ect.). You can store these addresses on a written book, for example. Arrange the runes in your keystone to match the rune address of your desired destination, and right click any gateway with the keystone. Assuming you are withing range, you will arrive at your destination instantly.
There can be as many different addresses as there are rune combinations. In short, the keystone (or lack thereof) in your hand determines where you can go, and the keystone in the gateway (or lack thereof) determines who can arrive.
|Gateways A, B and C are on the open network. Gateway D contains a Keystone with a Rune combination. Any person who activates and enters A, B or C will travel to the next in order. They will not be able to exit Gateway D. Anyone who enters gateway D will appear in gateway A, B, or C. Anyone who activates a gateway with a Keystone that matches the Keystone Receptacle in gateway D will travel to gateway D.|