The Tunnel of Eupalinos or Eupalinian aqueduct (Modern Greek: Efpalinio orygma, Ευπαλίνειο όρυγμα) is a tunnel of 1,036 m (3,399 ft) length in Samos, Greece, built in the 6th century BC to serve as an aqueduct. The tunnel is the second known tunnel in history which was excavated from both ends (Ancient Greek: αμφίστομον, amphistomon, "having two openings"), and the first with a geometry-based approach in doing so.