The famous Tunnel of Eupalinus, which is at Pythagoreio, was the " eighth wonder " of the ancient world. The way in which it is constructed often comes as a surprise even to modern experts. The success of the enterprise - given the means available at the time : the hammer and the chisel - is astonishing.

This tunnel is the middle section of a major, acqueduct, constructed around 550 B.C. by the architect Eupalinus, to supply the ancient city of Samos, the modern Pythagoreio, with water. Its construction took about ten years and the tunnel has a length of 1,036 metres. In order to construct the conduit, a total of 7,000 cubic metres of natural rock had to be removed. The section of the tunnel is on average 1.80 by 1.80 metres, and it cuts through the mountain at a depth of 180 metres below its summit.

This ancient tunnel is constructed with rectangular stones which are very skilfully fitted one on top of the other. It is roofed with a triangular vault, made with the same kind of stones. The persistence of the ancient Greeks, who in this section were faced with doubly difficult tasks, still calls forth the admiration of the visitor. They first had to hollow out the mountain and then construct in it the wall and vaulted corridor as a passageway.

The water was channeled through pipes which were installed in the acqueduct below the part of the tunnel in the direction of the source and alongside it in the direction of the town.

These pipes, which remain at many points, are so well made that they look as though they were put in yesterday, even after the passage of so many centuries - and all this without any of the technological means available to our own age.

The tunnel is lit and accessible to visitors.