Black sites were clandestine prisons or installations operated by powers such as the Romulan Star Empire, the Klingon Empire, and the Cardassian Union either presently or in the past. These prisoners were used to house prisoners or materials they considered too dangerous to be publicly acknowledged. In the United Federation of Planets the use of these types of clandestine prisons were explicitly forbidden under the Articles of Federation. During his time with Starfleet Intelligence Tuvok became aware of other Alpha and Beta Quadrant powers using such black sites.