"Babylon 5 is a fictional space station and the primary setting in the television series Babylon 5. Its design is a variation of an O'Neill cylinder.
Babylon 5 was designed as the "last, best hope for peace". It was the last of five stations to be built, with its predecessors either being destroyed by terrorists, or, in the case of Babylon 4, vanishing without a trace. The station is home to 250,000, including about 100,000 humans and 2,000 EarthForce personnel, and includes areas for business, accommodation and recreation.
The last of the Babylon stations, Babylon 5 was constructed ten years after the Earth-Minbari War. Its purpose was to "prevent another war by creating a place where humans and aliens could work out their differences peacefully". For this reason, it was situated in politically neutral space: in orbit around Epsilon III. It was a free port for a quarter of a million beings, and was co-funded by the Earth Alliance and Minbari Federation after the crippling financial loss of Babylon 4.
The year is 2258-62. The name of the place is Babylon 5."
Source: Wikipedia, "Babylon_5_(space_station)", available under the CC-BY-SA License.