The Maze prison houses most of the high-risk terrorists. Although the Northern Ireland Prison Service aims, so far as possible, to house all inmates together regardless of their terrorist connections, in the Maze prison there is a measure of de facto segregation for terrorists. At the Maze prison there is close perimeter security, with the military patrolling outside the prison and providing a backup force. Sensitive points in the prison are closely observed, and unarmed staff do not carry keys because of the risk that they may be taken. Security measures reduce the opportunities for large numbers of inmates to assemble. All inmates are allowed to wear their own clothes and to have weekly visits from their families, daily exercise periods, and association with other inmates. They also have regular opportunities to participate in sports and education.