The core of the Imperial Guard was the all volunteer Javidan Guard (Gârd e Jâvidân, Persian: Immortal Guard), better known as the “Immortals” after the ancient Persian royal guard or Persian Immortals. The “Immortals” were based in the Lavizan Barracks in northern Tehran. By 1978 this elite force comprised a brigade of 4,000-5,000 men, including a battalion of Chieftain tanks. It was responsible for the internal and external security of the royal palaces. A special plain-clothes unit was called Ma’mourin Makhsous (Special Agents)