Tunnel of the Eupalinos

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Coordinates: 37 ° 41 ′ 38 "  N , 26 ° 55 ′ 48"  E

Tunnel of the Eupalinos

The Eupalinos tunnel is part of an aqueduct that was built in the 6th century BC. To supply the Greek city of Samos (today: Pythagorio ) was built on the island of the same name . The tunnel is the second known tunnel in history to be built using the opposite direction , and the first to be built according to a carefully worked out plan. At 1036 meters in length, the Eupalinos Tunnel was also the longest tunnel of its time. Today it is a tourist attraction and its entire length can be walked from the south entrance. There are guided tours to the point where the two excavations met (and back to the south entrance) or to the north entrance (and not back again).

construction

The Eupalinos Tunnel is named after its architect Eupalinos von Megara , whose name was passed down to posterity by the Greek historian Herodotus (482–424 BC). In addition, nothing is known about the person of Eupalinos. It was speculated that the Greek philosopher and mathematician Pythagoras of Samos (approx. 580–500 BC), who was in his hometown at the time of the construction of the aqueduct and whose Pythagorean geometry might have been used, was involved, However, there is no concrete evidence of this.

The tyrant Polykrates of Samos (ruled 537-522 BC) is traditionally named as the builder of the tunnel in the older specialist literature . However, more recent research that Hermann Kienast from the German Archaeological Institute, Athens (DAI) carried out on the tunnel and which included the entire complex for the first time, suggests a slightly earlier completion date (between 550 and 530 BC). Estimates of the construction period range from 8 to 15 years, with Kienast assuming a construction period of around 10 years. In total, the aqueduct was in operation for more than a thousand years until it was neglected and finally abandoned in the 7th century AD.

exploration

Entrance to the tunnel

The rediscovery of the tunnel by a local abbot in 1882 goes back to Herodotus, who was the first (and only) ancient writer to report on the tunnel and to describe it with enthusiastic words ( Histories 3, 60):

“I dealt with the Sami for a little longer because they performed three of the greatest structures of all Greeks: They pierced a mountain 150 fathoms from below and dug a tunnel with two openings. Its length is seven stages, its height and width eight feet each. Another canal runs through its length, twenty cubits deep and three feet wide, through which the water is carried in pipes to the city; he comes from a strong source. The builder of this tunnel was Eupalinos from Megara, son of Naustrophos. This is one of the three structures ... "

Archaeological research into the aqueduct has since been promoted primarily by the DAI. In 1883 the German archaeologist Ernst Fabricius was the first to take a scientific inventory. After that, the tunnel was neglected again for almost a century until it was completely cleared and made accessible for exploration in 1971-73 by the DAI Athens under Ulf Jantzen . The building researcher Hermann Kienast published the final study of the entire complex in 1995. Other authors have mainly dealt with the question of how Eupalinos managed to bring the two drives together so precisely.

Overall system

The Eupalinos tunnel is the middle part of a water pipe that connected the city of Samos with the Agiades spring and crossed the 230 meter high city wall mountain. The aqueduct can be divided into three sections:

  • A 900 meter long underground pipe from the source to the north slope of the mountain. This section was outside the city walls.
  • The 1036 meter long Eupalinos Tunnel, which crosses the ridge in its entire width 180 meters below the summit.
  • A 500 meter long underground pipe from the southern slope of the mountain to a well house in the city area. This section was within the city walls.

The reason for the underground course of the aqueduct was probably the fear that the city's water supply could otherwise easily be cut off from the outside in the event of a siege. A total of around 7,000 cubic meters of natural rock had to be excavated for the construction, of which 5,000 cubic meters were accounted for by the tunnel, which had to be driven through solid limestone rock. With an average height of 1.80 meters and a width of 1.80 meters, the tunnel has practically a square cross-section. Only hammer and chisel were used as tools during the drive.

Conduit

Tunnel with the up to 8 m deep, modern barred water supply channel

The Eupalinos tunnel has practically no gradient. Its exit point is just like its entry point at 55 meters above sea level. A second, narrower pipe, which was cut into the ground on the east side of the tunnel and on the bottom of which the actual water pipe ran, provided the necessary gradient towards the city. This canal is almost 4 meters deep at the entrance of the tunnel into the mountain and reaches a depth of 8.90 meters at the tunnel exit. This enormous depth is explained by the fact that the spring level had already sunk in the course of construction, so that the water-bearing channel had to be laid deeper.

The reason for the double construction of tunnel and conduit, which can also be found in other tunnels of the time, is assumed to be constraints on measurement technology. Since “at that time there were no adequate measuring instruments to determine a gradient of less than 1%, but instruments like the Chorobates were able to keep the horizontal plane”, Eupalinos must first have been concerned with the two To bring drives together safely in the mountain. Once the two tunnels were connected, the second step was to knock out the necessary slope from the tunnel floor without having to take the risk that the two drives would miss each other.

Opposite driving

The builder Eupalinos had to determine two things with the greatest possible precision so that the two teams met in the mountain:

  • the level of inputs;
  • the direction of advance.

Both problems were masterfully solved by Eupalinos, as the construction of the tunnel reveals. The tunnel floor at the connection point between the north and south tunnels has a height difference of only 60 centimeters, which corresponds to a difference of less than 0.125 percent in relation to the total length of the tunnel.

However, it is unclear why the two tunnels meet almost at right angles, because if the two teams had kept the original, dead straight driving direction, the two halves of the tunnel would have come together almost perfectly. It is noticeable that the north tunnel is the first to deviate from the ideal direction and after a few hundred meters in the mountain it begins to form wide zigzag arcs, whereas the south tunnel only makes a sudden bend to the right after 425 meters straight to the north connect to. One reason for the changes in direction in the north tunnel could have been to bypass water-bearing layers or soft rock that would have meant a risk of collapse. The bend in the south tunnel should therefore be interpreted as a reaction to the change of direction in the other tunnel. It would also be conceivable and not entirely illogical to interpret the multiple slight changes in direction in the straight line as a consideration from the defense strategy, because kink points, even those of a slightly curved type, always represent a "protective shield" against attackers coming from the other direction.

Simple but effective was the method by which Eupalinos ensured that the two tunnels would meet. By making both drives turn sharply to the east for the last few meters, he counteracted the danger of digging two parallel tunnels and made a cutting point unavoidable if both tunnels were on the same level, which was the case. Top view:

Eupalinos' draft of the aqueduct, horizontal cross-section

The almost right-angled meeting and the slight difference in height between the two tunnels are considered in the scientific discussion as clear evidence of the first planned counter-site excavation in history. The fact that not a single vertical shaft has been dug over the entire 1036 meters also clearly separates the Eupalinos Tunnel from the Qanat construction method and makes it the longest tunnel of its time.

Surveying method

Given the precision of the Eupalinos Tunnel, modern science has been concerned with the question of which surveying methods the ancient builder might have used when tunneling through the mountain. Since Herodotus left no information about this, the scientists are dependent on archaeological evidence and mathematical calculations. The focus is on the question of how Eupalinos determined the level of the entrances and the direction of advance. Two approaches can be distinguished:

  • Surveying around the mountain (Heron of Alexandria, Apostol);
  • Surveying over the mountain (Goodfield & Toulmin).

The problem with both paths is the accumulated measurement inaccuracy, which, given the length of the tunnel, can very easily lead to the two tunnels missing each other in the mountain. The first scientist to come up with a mathematical solution for building a tunnel in the opposite direction was Heron of Alexandria ( Dioptra , Chapter 15). His theoretical approach was long considered to be the method that Eupalinos must have used until Goodfield & Toulmin encountered considerable topographical difficulties with horizontal bearings along the mountain while visiting the site in the 1960s. Therefore, instead, they favored surveying using escape poles over the ridge. The mathematician Tom Apostol , however, considers this method to be too error-prone due to the large number of individual measurements and considers the measurement around the mountain using simple auxiliary instruments to be practicable.

Notes and individual references

  1. ↑ The oldest known tunnel in which the drive was tackled from two sides at the same time is the Hezekiah tunnel in Jerusalem (around 700 BC). However, the numerous blind tunnels, which lengthen the total length of the tunnel by a third, indicate that no special scientific method was used to determine the heading direction (Burns, Alfred, p. 173). Presumably one simply followed the course of a water vein (Apostol, Tom, p. 33).
  2. ↑ Histories of Herodotus 3, 60
  3. ↑ Goodfield, June & Toulmin, Stephen, p. 46
  4. ↑ a b Evans, Harry B., Review of Hermann Kienast, p. 150
  5. ↑ a b c d Apostol, Tom, p. 38
  6. ↑ Evans, Harry B., Review of Hermann Kienast, p. 149
  7. ^ Apostol, Tom, p. 40
  8. ^ Apostol, Tom, p. 31
  9. ^ Burns, Alfred, p. 183
  10. ↑ Goodfield, June & Toulmin, Stephen, p. 47
  11. ↑ Burns considers both approaches to be possible (Burns, Alfred, p. 183)

literature

  • Tom M. Apostol : The Tunnel of Samos. In: Engineering and Science , No. 1 (2004), pp. 30–40 ( PDF )
  • Alfred Burns: The Tunnel of Eupalinus and the Tunnel Problem of Hero of Alexandria. In: Isis , Vol. 62, No. 2. (Summer 1971), pp. 172-185
  • Harry B. Evans: Review by Hermann Kienast, The water line of the Eupalinos on Samos. In: American Journal of Archeology , Vol. 103, No. 1. (Jan. 1999), pp. 149-150
  • June Goodfield, Stephen Toulmin: How Was the Tunnel of Eupalinus Aligned? In: Isis , Vol. 56, No. 1. (Spring, 1965), pp. 46-55
  • Ulf Jantzen (Ed.): The water pipe of the Eupalinos. The finds (Samos XX) . Rudolph Habelt Verlag, Bonn 2004, ISBN 3-7749-3312-X
  • Hermann J. Kienast: The aqueduct of the Eupalinos on Samos German Archaeological Institute Athens (information brochure)
  • Hermann J. Kienast: The water line of the Eupalinos on Samos. (Samos XIX), Rudolph Habelt Verlag, Bonn 1995, ISBN 3-7749-2713-8
  • BL Van der Waerden: Eupalinos and His Tunnel. In: Isis , Vol. 59, No. 1. (Spring 1968), pp. 82-83

Web links

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