The Tunnel of Eupalinos or Eupalinian aqueduct () is a tunnel of length running through Mount Kastro 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 (, "having two openings"), and the first with a geometry-based approach in doing so. Today it is a popular tourist attraction. The tunnel is inscribed on the UNESCO World Heritage List along with the nearby Pythagoreion and Heraion of Samos, and it was designated as an International Historic Civil Engineering Landmark in 2017.
Early history
The Eupalinian aqueduct is described by Herodotus (Histories 3.60), without whom it might not have been discovered:
I have dwelt longer upon the history of the Samians than I should otherwise have done, because they are responsible for three of the greatest building and engineering feats in the Greek world: the first is a tunnel nearly a mile long, eight feet wide and eight feet high, driven clean through the base of a hill nine hundred feet in height. The whole length of it carries a second cutting thirty feet deep and three broad, along which water from an abundant source is led through pipes into the town. This was the work of a Megarian named Eupalinus, son of Naustrophus.
The tunnel might also be referred to in the Homeric Hymn to Apollo, which mentions "watered Samos." The tunnel was dug in the mid-sixth century BC, by two groups working under the direction of the engineer Eupalinos from Megara, in order to supply the ancient capital of Samos (today called Pythagoreion) with fresh water. This was necessary for demographic reasons: the city of Samos had outgrown the capacity of the wells and cisterns within the city's limits, but the main source of fresh water on the island was on the other side of Mount Kastro from the city. It was of the utmost defensive importance; because the aqueduct ran underground, it could not easily be found by an enemy, who might otherwise cut off the water supply. The date of construction is not entirely clear. Herodotus mentions the tunnel in the context of his account of the tyrant Polycrates, who ruled c. 540–522 BC, but he does not explicitly say that Polycrates was responsible for its construction. Aideen Carty suggests that it should be connected with the regime that overthrew the Geomori in the early sixth century BC, which granted citizenship to a large number of Megarians, perhaps including Eupalinos. The Eupalinian aqueduct was used as an aqueduct for 1100 years, before it began to silt up. In the seventh century AD, the south end was used as a defensive refuge.
Description
Spring and reservoir
The tunnel took water from an inland spring, located about above sea level near the modern village of Ayiades. It discharges about 400 m3 of water per day. This spring was covered over. Two rectangular openings, each measuring , feed the water into a large reservoir with a roughly elliptical ground plan. Fifteen large stone pillars support a roof of massive stone slabs. The spring was thus completely concealed from enemies. The construction of this reservoir seems to have caused the outlet of the spring to subside by several metres. At some point before the nineteenth century, a church dedicated to St John was built over the top of this reservoir, further hiding the spring's location.
North channel
From the spring, a buried channel winds along the hillside to the northern tunnel mouth. The channel is long, although the distance from the spring to the tunnel mouth as the crow flies is only . The channel is wide and about deep. After it had been cut out of the bedrock, it was covered over with stone slabs and then buried. There are inspection shafts at regular intervals along the channel's course. The last of this channel pass under a small hill. Vertical shafts were dug from the surface at intervals of and then linked up to create a short tunnel, which brings the water.