Hardly anything is known of Nicomachus of Gerasa (nuh-KAHM-uh-kuhs of JEHR-uh-suh) beyond his surviving works. His Arithmītikī eisagōgī (n.d.; Introduction to Arithmetic, 1926) is a general textbook that synthesizes the metaphysics of Plato and Pythagoras, emphasizing mathematics. His Enchiridion harmonikīs (n.d.; Handbook of Harmony, 1967) is also primarily a work of metaphysics. His Theologoumena arithmetikīs (n.d.; theology of arithmetic) survives only in fragments and in a summary by the ninth century Byzantine patriarch and scholar Saint Photius. Among Nicomachus’s lost works are a biography of Pythagoras, a geometry textbook, and perhaps an encyclopedia.