Zerzevan Castle (Kurdish: Qesra Zêrzevan, Zîrzevan Turkish: Zerzevan Kalesi Armenian: Զերզեվանի ամրոց), also known as Samachi Castle, is a ruined Eastern Roman castle, a former important military base, in Diyarbakır Province, southeastern Turkey. Archaeological excavations at the site revealed the existence of underground structures, among them a temple of Mithraism, a mystery religion. The castle was used as a civilian settlement between the 1890s and the 1960s. The site is partly open to tourism.