Tunnel of Eupalinos

Samos, located just off the coast of Turkey, is the eighth largest Greek island with an area of less than 200 square miles. The island flourished in the sixth century B.C. during the reign of the tyrant Polycrates, whose court attracted poets, artists, musicians, philosophers and mathematicians.  Eupalinos was the master builder/hydraulic engineer from Megara in mainland Greece retained to supply the ancient capital of Samos (near the modern town of Pythagoreio) with fresh water. Armed with only intellectual tools, he pulled off one of the finest engineering achievements of ancient times.

The island had a copious spring at a place called Agiades, but access to this source of water was blocked by the 900-ft Mount Castro.  Eupalinos’ solution was to dig a 3,400-ft-long unlined tunnel through the limestone mountain.  The tunnel was excavated by hand from both ends simultaneously with a horizontal floor since a sloping tunnel would have accumulated groundwater at its upper end of excavation. However, recognizing that water needs a gradient to flow, a 2-ft-wide aqueduct channel was excavated into the bedrock on one side of the tunnel with 0.36% slope down to a depth of 30 ft below the tunnel floor. Working conditions during excavation must have been extremely unpleasant with dust from rubble and smoke from oil lamps used for illumination likely presenting serious ventilation problems.

The technologically-advanced tunnel is a miracle of applied geometry and surveying engineering principles. Skillful as he was, Eupalinos was limited to the use of geometry, the straight surveying line, and techniques for measuring distance, altitude and angles. While water could have been brought around the mountain by an aqueduct, it is believed that a tunnel was used as a security consideration to protect the city’s water supply from enemies.

The project has several unique features and characteristics:

• It was the first known deep tunnel in history where vertical shafts were not used in its construction.
• The tunnel was conceived to follow a straight line in a mountainous terrain. However, deviations from the straight line were made to avoid poor quality rock material.
• Described by Herodotus in 440 B.C. for the first time in written literature, the tunnel was excavated from two end openings as is now done in modern construction practice.
• The two segments met at an astoundingly small elevation difference of only 2 ft!
• Hydraulic flow aspects were incorporated by cutting a sloping aqueduct channel into a side of the otherwise-level tunnel floor.

Construction started around 530 B.C. and lasted nearly ten years. The pipes in the tunnel transported water to the city for some 1,200 years. The tunnel also offered unique protection for the local people against pirate invasions and was used for long periods by the Samian people as a refuge. Considered to be one of the greatest engineering achievements of ancient times, the tunnel was declared as a UNESCO World Cultural Heritage Site in 1992 and an International Historic Civil Engineering Landmark by ASCE in 2017.

The southern half of the tunnel is lighted and is accessible to visitors.