The monastery was built by order of Emperor Justinian I (reigned 527–565), enclosing the Chapel of the Burning Bush (also known as "Saint Helen's Chapel") ordered to be built by Empress Consort Helena, mother of Constantine the Great, at the site where Moses is supposed to have seen the burning bush.[18] The living bush on the grounds is purportedly the one seen by Moses.[19] Structurally the monastery's king post truss is the oldest known surviving roof truss in the world.[20] The site is sacred to Christianity, Islam, and Judaism.[21]