2,500 Years Ago: Greeks Dug from Opposite Sides of a Mountain… How Did They Meet?

Two crews started on opposite sides of a Greek mountain, cut toward each other by hand in the dark, and met. The corner where they met was planned. The tunnel runs about 3,400 feet through Mount Kastro on Samos, and it carried the city's water for roughly 1,100 years. We go through the job step by step: why the water had to be hidden underground, how the engineer Eupalinos set his line before a single hammer fell, the two rival ideas about how he did it, and the painted marks that counted the tunnel off in fifty equal steps. Then comes the part engineers still recognize. Near the meeting point he raised one ceiling, dropped one floor, and bent both tunnels so they would cross instead of running side by side forever. When the two halves met, their floors were within about two feet of each other. The same problem came back in 1866 at the Hoosac Tunnel, and again in 2010 under the Alps. SOURCES AND FURTHER READING Hermann J. Kienast's survey, Die Wasserleitung des Eupalinos auf Samos, 1995, with his measurements summarised here: https://en.wikipedia.org/wiki/Tunnel_... Tom Apostol, The Tunnel of Samos, Engineering and Science, Caltech, 2004: https://webs.um.es/pherrero/apostol_e... Fred Roeder, The Tunnel of Eupalinos, LIDAR Magazine, 2009, the article behind the finished-by-ear idea: https://lidarmag.com/2009/04/11/the-t... The tunnel's restoration project, with the water figures and the visiting information: https://www.eupalinos-tunnel.gr/ American Society of Civil Engineers landmark page for the tunnel: https://www.asce.org/about-civil-engi... Hoosac Tunnel, including the alignment towers and the 1872 breakthrough: https://en.wikipedia.org/wiki/Hoosac_... Which parts are settled and which parts are still argued over, I say out loud in the video. This channel takes one thing people built before machines and shows how they did it. Subscribe if that is your kind of thing. Good one to watch next: the Babylonian tablet that did an integral before Newton. CHAPTERS 0:00 Two crews, one mountain, and a corner 1:15 The number that would have ruined everything 1:50 How Jerusalem did it two centuries earlier 2:16 Why the water had to be hidden 3:09 The trench nobody expects 4:28 Around the mountain, or over the top 6:50 A decade of five-inch days 8:23 The notch that fixed a wrong turn 9:01 Wet rock, and the triangle detour 11:26 Raise a ceiling, drop a floor 12:38 The bend that made missing impossible 13:34 Massachusetts solves it again in 1866 15:32 Did they finish by ear? 16:40 The last thin wall of stone