Quarto was one of ten planets in the Trafalgar System, and the only one inhabited by the Terrans. It once hosted a population of millions.
In 2669, the Kilrathi Empire launched a biological attack on Trafalgar, infecting the entire population of Quarto. The planet was a total loss and the entire star system was immediately quarantined. Despite this enormous loss, however, Trafalgar retains an active government, and the survivors of the attack reside in the asteroids as miners.
By 2701, Quarto can only be accessed with bio-suits and is beyond recovery.