Monuments and memorials to the genocide of the Khmer Rouge era in the 1970s are the Tuol Sleng Genocide Museum (a former high school used as a concentration camp) and, on the outskirts of the city, the Choeung Ek Genocide Center. The Cambodia-Vietnam Friendship Monument was commissioned by the Vietnamese communists as symbol of Khmer-Vietnamese friendship during the late-1970s following the liberation of Cambodia from the Khmer Rouge.