Epsilon III is the third planet of the Epsilon Eridani system, in Euphrates Sector, Grid Epsilon. The primary jumpgate in the system is in high orbit above it. Early scans determined that the planet was seismically stable and entirely lifeless.
What the surveys failed to detect was an advanced piece of technology built deep within the planet centuries earlier by an unknown race. Guardians were chosen from the native population throughout the centuries, however those beings began slowly dying out, and in 1758, Varn, the last of his race, became the Guardian of the Great Machine.
Babylon 5 was built in orbit over Epsilon III in 2256. Until 2258, the planet was thought to be stable and uninhabited. Then, Varn the guardian of the Great Machine began to die which destabilised the machine and threatened to destroy the planet and endanger B5.
Draal, a Minbari, eventually took Varn's place and forbade access to the planet until the appropriate time. This appropriate time was a year later when Draal revealed himself - rejuvenated to his appearance of thirty years ago - to John Sheridan and Delenn. They journeyed down to Epsilon III to meet with Draal and establish the Great Machine as an ally of the Army of Light. At that time, he revealed that he was not alone on the planet; several caretakers lived there as well.
During the Shadow War, the Army of Light would make several trips to the planet. First, Susan Ivanova used the Great Machine to find the First Ones in preparation for the final stages of the war. Shortly thereafter, Draal used the Great Machine to open the temporal rift in Sector 14, allowing the White Star to go back in time and steal Babylon 4.
During the last days of the war, when the Vorlons and Shadows started destroying entire planets showing influence of the other race, refugees were turning up on Babylon 5 by the thousands. Dr. Stephen Franklin noted that Epsilon III had never been touched by either race. With permission from the Babylon 5 War Council, the doctor set up an emergency shelter and clinic unit in the tunnels leading down to the Great Machine to house them.
The last recorded visit of Babylon 5 personnel to Epsilon III was in 2261, when Ivanova visited the planet to recruit Draal and the caretakers' help in using the Great Machine to provide the power necessary to transmit the Voice of the Resistance broadcast during the Earth Alliance Civil War.
When Babylon 5 was decommissioned in 2281 to prevent it from becoming a navigation hazard, the wreckage from the demolition was caught in Epsilon III's gravity well and burned up in the atmosphere.