Babylon 4 was the fourth and largest space station built under the Babylon Project.
Partly constructed from materials recycled from the earlier Babylon stations, Babylon 4 also possessed engines that allowed the station to be moved from place to place, although this was a very slow process due to its size.
The station featured two carousels rotating in opposite directions, presumably balanced to bring the net rotation of the entire mass closer to zero, making it much easier to move and maneuver the station.
Reappearing in its original location in July 2258, the crew was rescued by Babylon 5 personnel, shortly after which the station disappeared again. Sector 14 was declared off-limits after these events.
After the crew was rescued, Jeffrey Sinclair took Babylon 4 to the Earth year 1260. Sinclair contacted the Vorlons Kosh Naranek and Ulkesh Naranek on his arrival and with them on board, he used the Chrysalis device to transform himself into a Minbari named Valen. Thus, Valen was "A Minbari not born of Minbari."
Arriving after the Minbari's base of operations had been destroyed during the First Shadow War, Valen provided the Minbari with Babylon 4 as their new headquarters. When the war was over, the station was abandoned.
For over 900 years the station lay dormant, guarded by the Tak'cha, who referred to it as Ende X'Ton ("the lost station") which they believed to be a holy place. In 2261 it was found floating adrift in Sector 730 by 12 by 9 by John Sheridan, Delenn, Michael Garibaldi, and Susan Ivanova. Within 48 hours of rediscovering the station, Babylon 4 burned up in the atmosphere of the planet it was orbiting.
At the time of its disappearance, Babylon 4 had not yet been assigned a permanent commanding officer; Major Lewis Krantz, an EarthForce Marine Corps officer, was assigned to oversee the final stages of construction.