Eupalinus’ aqueduct in Samos island is one of the greatest technical works of antiquity. Since its surface remnants disappeared when it ceased functioning, Herodotus’ reference to it offered scholars the incentive to look for and discover the tunnel in the nineteenth century. In 1881 attempts were made for the refunctioning of the main and for the research and documentation of the relevant installations. Eupalinus’ tunnel and especially its construction under a mountain soon became renowned and raised at the same time a number of questions and issues as regards its construction and building.