Babylon 4 was the fourth and largest space station built under the Babylon Project.
Babylon 4 was constructed from materials recycled from the earlier Babylon stations. Babylon 3 emblems could be found on some surfaces of the station.
Babylon 4 had engines and could move through space under its own power. It was also, to date, the most powerful station ever constructed by human hands.
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.
After the crew was rescued, Jeffrey Sinclair took Babylon 4 to the year 1260. During this temporal trip, Sinclair used the Chrysalis device to transform himself into a Minbari, named Valen. Thus Valen being named "A Minbari not born of Minbari."
Arriving after the Minbari base of operations had been destroyed during the First Shadow War, Valen provided the Minbari with Babylon 4 as the new base of operations in the war effort. When the war was over the station was abandoned.
The Tak'cha guarded Babylon 4, a location they believed was holy, for the thousand years it lay dormant until John Sheridan, Delenn, Michael Garibaldi, and Susan Ivanova found it floating adrift in early 2261. Within 48 hours of rediscovering the station, Babylon 4 burned up in the atmosphere of the planet it was orbiting.