Digging tunnels is probably among the most toughest engineering projects the ancient people undertook, because it required mastering several sophisticated fields of science including architecture, geodesy, hydraulics, and geology. This makes ancient tunnels fascinating subjects for study.

The Tunnel of Eupalinos, on the Greek island of Samos, is one such example. Built in the 6th century BC, and first described by Herodotus, the Tunnel of Eupalinos was a major engineering milestone because it is one of the earliest known tunnels that was dug from both ends. Using only picks, chisels and hammers, and relying on simple laws of geometry and trigonometry, these ancient engineers accomplished a nearly impossible feat—meeting beneath a hill more than two hundred meters tall and nearly half a kilometer from either end.

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