Male block of the siphon

Perforated limestone block of the inverted siphon pipe of the Aspendos aqueduct. This side is the 'male side' of the block. Notice the round smoothed surface around the central perforation that was used to make a waterproof seal; the outer edges of the squareblock were not part of this seal. Seljuk bridge on the Eurymedon. Photograph Cees Passchier