When the Greek engineer Eupalinos contrived a tunnel in the 6th century B.C. to carry water through Mount Kastro to Samos, he started digging simultaneously from the north and south, hoping that the two tunnels would meet in the heart of the mountain. He arranged this through some timely doglegs: When the two teams could hear one another (meaning they were about 12 meters apart), each deviated from its course in both the horizontal (left) and vertical (right) planes:

Source: The Tunnel of Eupalinos – Futility Closet

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I’d heard about this decades ago in injineering skrule.  But didn’t realize the enormity of the undertaking.

Guess that’s why I never “grokked” the importance of civil engineering.

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