Opus (also Opous), in Ancient Greece, the chief city of Opuntian or Eastern Locris. It was located on the northern coast of mainland Greece opposite Euboea, perhaps at modern Atalandi . Its harbor was at Cynus. In the Iliad, Homer mentions Opus as one of the Locrian cities whose troops were lead by Ajax the Lesser, son of Oileus the king of Locris (Homer, Iliad, 2.525-530). Pindar's ninth Olympian ode, concerns Opus. Opus fought on the Greek side at Thermopylae, but surrendered, joining the Persians, and on the Spartan side during the Peloponnesian War. In 198 BC, during the Second Macedonian War they went over to the Romans.