ZATO, closed city or closed town is a settlement where travel and/or residency restrictions are applied so that specific authorization is required to visit or remain overnight.
They may be sensitive military establishments or secret research installations which require much more space or freedom than is available in a conventional military base. There may also be a wider variety of permanent residents including close family members of workers and/or trusted traders who are not directly connected with its obscured purposes.
Closed cities are a feature of heavily militarized countries and secretive regimes, and many still exist in the successor countries to the Soviet Union. In modern Russia, such places are officially known as "closed administrative-territorial formations" (закрытые административно-территориальные образования, zakrytye administrativno-territorial'nye obrazovaniya, or ЗАТО ZATO for short).
