The Tunnel of Eupalinos is a mastery of Greek engineering that took place during the 6th century bce. Located on the Isle of Samos, it was constructed as a 1,000+ meter tunnel through Mt Kastro as an underground aqueduct that would bring the vital resource to the capital, now known as Pythagoreion.
The true beauty of this undertaking, is that it was a tunnel known as an amphistomon,
"having two openings." Basically, instead of a traditional tunnel started on one side, tunneling to the other, it had simultaneous openings on both ends that met miraculously in the middle.
Exactly which principles of geometry did Eupalinos use, how did he survey it properly, and how did his teams mine through the limestone with such precision?