(Greek: Αρχαία Θήρα) is an antique city on a ridge of the steep, 360 m high Messavouno mountain on the Greek island of Santorini.
It was named after the mythical ruler of the island, Theras, and was inhabited from the 9th century BCE until 726 CE. Starting in 1895 the city was systematically investigated by Friedrich Hiller von Gaertringen, who excavated there until 1904. Later excavations by N. Zapheiropoulos between 1961 and 1982 under the auspices of the Archaeological Society of Athens unearthed the city’s necropolis in Sellada. Findings from these excavations are on exhibit at the archaeological museum in Fira.