How it began
The tunnel was cut on the Aegean island of Samos in the sixth century BCE to bring water to the capital of the tyrant Polycrates from springs on the far side of Mount Kastro. Herodotus names the builder as the engineer Eupalinos of Megara. The ancient capital is today called Pythagoreio. Two groups dug toward each other from opposite sides of the mountain in the middle of the century, working under his direction.
How it works
The bore is about two meters across and more than 914 meters long. It was driven through the rock with hammers and chisels by teams of enslaved workers. To save time the tunnel was advanced from two headings at once. Britannica records that the two bores did not line up exactly and that the junction was made by a turn in the middle. It is the second known tunnel in history to be dug from both ends, and the first in which the builders used a geometry-based approach to make the two halves meet.
What changed first
The tunnel gave the city of Polycrates a supply of fresh water that came through the mountain, out of sight, from springs on the other side. Herodotus thought it worth recording along with the name of its engineer, which is why Eupalinos is known today. Britannica counts it among the major feats of ancient engineering.
What lasted
The aqueduct worked for more than 1,000 years. Its method, starting from both sides and steering two headings to a meeting point inside the rock, is what sets it apart in the record: it is the second known tunnel dug from two ends and the first in which a geometry-based approach was used to do so. The slight misalignment that Britannica reports, corrected by a turn in the middle, shows the limits of the surveying available to Eupalinos as well as its reach. The tunnel survives beside the town of Pythagoreio, and visitors can walk its entire length.
