Anatolia Antiqua XX (2012), p. 25-34

Âke OLSON*

HOW EUPALINOS NAVIGATED HIS WAY THROUGH THE MOUNTAIN

An empirical approach to the geometry of Eupalinos' tunnel on Samos

Introduction

The Eupalinos tunnel was cut from both ends, ca. 1040 m through the Kastro mountain on Samos, around 550 to 540 B.C. and it has fascinated people ever since. The construction carried drinking water from the spring at Ajades some few kilometres north of the ancient city of Samos (modern Pythagoreion) through the mountain north of the city. The tunnel consists of two parts, a north and a south part, obvi¬ ously cut from both ends. The two tunnel sections meet below the summit of the mountain, which rises to 225 m above mean sea level. The total length of the tunnel is ca. 1040 m divided into 612 m for the north part and 424 m for the south part1. The cross-section of the tunnel measures ca. 1.8 x 1.8 m. The floor of the tunnel is almost perfectly flat at ca +55 m. In the tunnel a qanat-like technique has been used for a deep trench with the water pipes at the bottom. Water entered in the north at +5 1 2 m and left in the south at +47.7 m giving a tilt of 0.36 %. The width of the qanat varies from 0.6 m to 0.8 m. North of the tunnel water was carried, first in a ditch covered with stone slabs and later, before reaching the entrance of the tunnel, a qanat-like technique was used. The construction ends on the south side with an arrangement for distributing water into the city. The total length of the pipe line from the spring to the end in the city is about 3 km using more than 4000 pipes. The inner cross-section of the pipe measures 0.24 to 0.26 m. The capacity has

been estimated at 400 cubic meters per 24 hours, equal to ca. 5 litres per second.

During construction that probably reached over more than one decade a serious problem arose. When starting the north tunnel it was soon obvious that the material in the mountain was very weak with collapsing walls and roof2. This problem was to some extent solved by supporting walls inside the tunnel. But about 270 m into the mountain Eu¬ palinos gave up the straight line and deviated the tunnel to the west to find better material to work in. Further on it was apparently considered safe to turn back towards the original line. Before the rendezvous of the two tunnel sections the north tunnel zigzags, however, in a most challenging way. How Eupalinos here navigated is indeed intriguing.

In this paper I argue that the only geometrical component planned to be used by the constructor was the straight line. Because of unforeseen obstacles the tunnelling had to be deviated and for geometrical reasons an equal-legged triangle was used for the navigation. Doing this, different errors were introduced by mistake, which led the tunnelling to a more eastern course. This was later corrected, obviously after a remeasurement, bringing the tunnelling back to the originally chosen straight line. Kienast maintains that it was planned by Eupalinos to secure the south and north tunnels to hit each other by way of a "ten¬ tacle" under the summit of the mountain3. In my opinion it is only a coincidence that the two tunnels meet each other close to the summit. I argue that the