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. Today it is a popular tourist attraction.

Historical data

In the sixth century BCE, Samos was ruled by the famous tyrant Polycrates. During his reign, two groups working under the direction of the engineer Eupalinos from Megara dug a tunnel through Mount Kastro to build an aqueduct to supply the ancient capital of Samos (today called Pythagoreion) with fresh water. This was of utmost defensive importance, as the aqueduct ran underground it was not easily found by an enemy who could otherwise cut off the water supply. The Eupalinian aqueduct was used for a thousand years, as proved from archaeological findings. It was rediscovered in 1882-1884 and today is open to visitors.

Eupalinos (Ancient Greek: Εὐπαλῖνος) or Eupalinus of Megara was an ancient Greek engineer who built the Tunnel of Eupalinos on Samos Island in the 6th century BC.

The tunnel, presumably completed between 550 and 530 BC, is the second known tunnel in history which was excavated from both ends and the first with a methodical approach in doing so. Being also the longest tunnel of its time, the Tunnel of Eupalinos is regarded as a major feat of ancient engineering. It was constructed for the tyrant Polycrates of Samos, and was a remarkable 1,036 meters (3,399 ft) long. It brought water to the city, passing through limestone at the base of a hill; this tunnel still exists.

The Greek historian Herodotus describes the tunnel briefly in his Histories (3.60) and calls Eupalinos of Megara its architect:

Eupalinos is supposed to be the first hydraulic engineer in history whose name has been passed down. Apart from that, though, nothing more is known about him.

A large road tunnel, named after Eupalinos has been recently built under the Geraneia mountains in Corinthia, to facilitate the new expressway connection between Athens and Corinth. Eupalinos tunnel is the longest of three subsequent tunnels of the same width at this expressway.