Tunnel of Eupalinos, Ancient tunnel in Samos, Greece
The tunnel of Eupalinos is an ancient water supply system inside Mount Kastro on the island of Samos in Greece. The system consists of two levels: an upper passage for maintenance and inspection, and a lower channel through which spring water flowed to the city of Pythagoreion.
Between 550 and 530 before Christ, the tyrant Polycrates ordered this tunnel to be dug to supply his capital with water from a distant spring. Two teams started simultaneously on opposite sides of the mountain and met almost perfectly in the middle after years of hard work.
The name honors the engineer Eupalinos from Megara, whose geometric method allowed both digging teams to align precisely. Visitors can still see chisel marks along the walls, showing how ancient workers carved through the limestone from both sides at the same time.
The entrance sits near Pythagoreion and can be reached by a short walk, with sturdy shoes needed for the slippery ground. Guided tours last about an hour and cover the lit section, while the rest of the tunnel remains closed to the public.
The two teams missed each other at the breakthrough by less than 1 meter (about 3 feet) horizontally and only a few centimeters vertically. Archaeologists discovered in the 19th century the remains of tools and oil lamps left behind during construction.
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