The Iconian gateway was a technology developed by the ancient Iconians, whose underlying principles remain well beyond Federation science. The gateway allowed instantaneous travel over enormous distances, at least 70,000 light years. Physically the gateway appeared literally as a "door", either suspended in space or surrounded by a frame, through which was the destination. An individual could simply step through the gateway (as they would an ordinary door) and emerge on the other side. The gateway network allowed the Iconians to travel throughout the galaxy without the use of starships and was the chief means through which they controlled their vast empire, earning them a reputation among their primitive subject peoples as "Demons of Air and Darkness."
Only two Iconian gateways were known to have survived the destruction of the Iconian civilization, both of which were later destroyed. The first was found in 2365 inside the only remaining structure on the surface of Iconia, and was accidentally activated by Lieutenant Commander Data as he was investigating the Iconian controls. The gateway apparently acquired possible destinations automatically, including the USS Enterprise-D and the Haakona. The Enterprise-D away team used the gateway to escape, destroying the facility behind them to prevent it from falling into Romulan hands. (TNG: "Contagion")
The second gateway was discovered in 2372 by the Dominion inside a stone ziggurat on the planet Vandros IV in the Gamma Quadrant. A group of renegade Jem'Hadar seized the gateway for themselves and re-activated it using equipment stolen from Deep Space 9. It was believed that they intended to use the gateway to foment an insurrection and mount a takeover of the Dominion. If they succeeded, the rogue Jem'Hadar would then gain the ability to move a force of any size onto any planet in the Federation or Dominion alike. Therefore, a joint Starfleet-Jem'Hadar team, led by Benjamin Sisko and Omet'iklan, successfully retook and destroyed the gateway. This second gateway generated some type of interference that prevented the functioning of energy weapons in its vicinity.
|Places seen through the Iconian gateway on Iconia|
|Places seen through the Vandros IV gateway|
The discoveries of more Iconian gateways is the backbone of the Star Trek: Gateways novel miniseries.
According to Star Trek Online, the Iconian gateways constitute a galaxy-spanning network of thousands of gateways of various sizes, including ones large enough to admit fleets of starships. The network also extends towards the Andromeda Galaxy, though to what extent is unknown. It's also revealed that the Iconians do utilize spacecraft. These vessels are able to open ship-sized gateways at will, using them to travel great distances instead of traditional warp drives.