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Tunnel of Eypalinos “I have dwelt the longer on the affairs of the Samians, because three of the greatest works in all Greece were made by them. One is a tunnel, under a hill one hundred and fifty fathoms high (274.32 meters), carried entirely through the base of the hill; with a mouth at either end. The length of the cutting is seven furlongs (1407 metres)the height and width are each eight feet (2,4 metres). Along the whole course there is a second cutting, twenty cubits deep (13 metres) and three feet broad (0,9 metres), whereby water is brought, through pipes, from an abundant source, into the city. The architect of this tunnel was Eupalinos, son of Naustrophus, a Megarian.” Herodotus, Histories, III
Historical data
The aqueduct was built in Samos, in the sixth century BC, during the reign of the tyrant Polycrates. Two groups working under the direction of the engineer Eupalinos from Megara dug a tunnel through Mount Kastro to build an aqueduct to supply the ancient capital of Samos (today called Pythagoreion) with fresh water. Because the aqueduct ran underground, it could not easily be found by an enemy, who might otherwise cut off the water supply. The Eupalinian aqueduct was used for a thousand years, as proved from archaeological findings. It was rediscovered in 1882-1884 and today is open to visitors. In 1992 UNESCOdeclared the area of Eupalinos Aqueduct a World Cultural Heritage site.
Description of the aqueduct The aqueduct has a total length exceeding 2,5 km. It started from the Ayiades spring, the “great spring” according to Herodotus, where water was collected in a rectangular reservoir covered by stone slabs. The water was transferred from the reservoir through an underground clay pipe to the northern entrance of the tunnel. It was carried from the tunnel’s southern exit to reservoirs and fountains in the ancient city via a pointed underground built channel with manholes at intervals. The central section of the aqueduct, consists of the “Eupalinos tunnel” within with the water was channeled through clay pipes, parts of which are still visible. The tunnel is 1036m long. It consisted of a corridor having internal dimensions 1.80x1.80m and of a ditch 0.60m wide (see figure 2). The depth of the ditch ranged from 4.0m in its northern section to 8.9m in its southern one, to ensure gravitational water flow. The maximum overburden of the tunnel is ~ 170 m below the summit of the
mountain and its elevation is 55m above sea level. The majority of the tunnel is unlined, while 230m were lined with high quality faced stones (see figure 1).
Figure 1: Archaic (left) & Roman (Right) tunnel linings
Corridor
Ditch
Figure 2: Corridor and ditch of the tunnel
Construction process Eupalinos used three straight lines for his navigation. First he constructed a “mountain” line, over the mountain at the easiest part of the summit. He connected a “south line” to the mountain line at the south side going straight into the mountain around which Eupalinos undulated the south tunnel. At the north side a “north line” is connected to the mountain line. This line guided the cut into the mountain from the
north side. The tunnel was hewn out simultaneously from both sides, and two crews of stonemasons, working with hammers and chisels, met with almost no deviation. The digging had to be checked continuously to ensure that it remained straight as well as horizontal. For this purpose lanterns were placed on the floor axis. The straightness of the dig was constantly monitored with a diopter. The poles on the slope showed the straight line that the tunnel axis should follow. Moreover, the chorobates, using a water level continuously checked the tunnel floor for levelness. The north and south halves of the tunnel meet in the middle of the mountain at a dog-leg, a technique to assure they did not miss each other. In planning the dig, Eupalinos used now well-known principles of geometry, codified by Euclid several centuries later. When it comes to measurements, he used a unit of 20.59 meters for distance measurements and 7.5 degrees (1/12 of a right angle) for setting out directions. Eupalinos was aware that errors in measurement and staking could make him miss the meeting point of the two teams, either horizontally or vertically. He therefore employed the following techniques. ďƒ˜ In the horizontal plane; The tunnel has a width of approximately 1.8 by 1.8 metres (5.9 by 5.9 ft). Eupalinos calculated the expected position of the meeting point in the mountain. Knowing that two parallel lines never meet, Eupalinos recognized that an error of more than two meters (6.6 ft) horizontally meant that the north and south tunnels would never meet. Therefore he changed the direction of both tunnels, as shown in the picture (one to the left and the other to the right), so that a crossing point would be guaranteed, even if the tunnels were previously parallel and far away.
Figure 3: Technique in the horizontal plane
ďƒ˜ In the vertical plane; Similarly, there was also a possibility of vertical deviations and, again, Eupalinos could not take a chance. He increased the possibility of the two tunnels meeting each other, by increasing the height of both tunnels. In the north tunnel he kept the floor horizontal and increased the height of the roof, while in the south tunnel he kept the roof horizontal and increased the height by changing the level of the floor. His precautions as to vertical deviation proved unnecessary, however, since measurements show that there was very little error; Kienast reports a vertical difference in the opening of the tunnels of only four centimeters (1.6 in).
Figure 4: Technique in the vertical plane
After 273 meters Eupalinos directed the northern tunnel to the west, obviously because of a combination of water, weak rock and mud. When leaving the north line Eupalinos used for navigating an equal-legged triangle with angles 22.5, 135 and 22.5 degrees in theory. Measuring errors occurred and were handled by Eupalinos within the accuracy he could obtain. The cutting of the south tunnel was stopped after 390 metres for the north tunnel to catch up. For the rendezvous of the two tunnels a tentacle was applied at the head of the south tunnel, giving 17 metres wider catching width (technique followed in the horizontal plane). When the two tunnels reach within earshot, the tunnels are directed towards each other and meet at a nearly right angle. This took place almost under the summit, but that was coincidental. He underestimated his measuring accuracy because, before the rendezvous, he raised the ceiling of the north tunnel by 2.5 m and lowered the floor of the south tunnel by 0.6 m, giving him a catching height of almost 5 metres (technique followed in the vertical plane). At the rendezvous, the closing error in altitude for the two tunnels was a few decimetres.
Figure 5: Floor plan of the tunnel
Sources: https://en.wikipedia.org/wiki/Tunnel_of_Eupalinos http://www.eupalinos-tunnel.gr/ https://www.youtube.com/watch?v=CR8BIMxrorA&t=183s