It is an underground tunnel 1.036 meters long that was built as part of the aqueduct of Samos for the installation of a clay drinking water pipeline under the mountain of the citadel of Samos. It is an unsurpassed technical work of antiquity in the field of topography and hydraulic art as it was opened simultaneously by both spouts which (after some deliberate changes of direction due to the nature of the subsoil) joined at the planned point below the top of the mountain. The main part of the trench is of square cross section (1,80m*1,80m) and includes an additional deep trench 0,90 m wide and deep 3,80 to 8,50 m. Herodotus, who describes the work with admiration, attributes it to the architect Eupalinus from Megara.