Tunnel Of Eupalinos
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The Tunnel of Eupalinos or Eupalinian aqueduct ( el, Ευπαλίνιον όρυγμα, translit=Efpalinion orygma) is a
tunnel A tunnel is an underground passageway, dug through surrounding soil, earth or rock, and enclosed except for the entrance and exit, commonly at each end. A pipeline is not a tunnel, though some recent tunnels have used immersed tube cons ...
of length running through Mount Kastro in
Samos Samos (, also ; el, Σάμος ) is a Greek island in the eastern Aegean Sea, south of Chios, north of Patmos and the Dodecanese, and off the coast of western Turkey, from which it is separated by the -wide Mycale Strait. It is also a separate ...
,
Greece Greece,, or , romanized: ', officially the Hellenic Republic, is a country in Southeast Europe. It is situated on the southern tip of the Balkans, and is located at the crossroads of Europe, Asia, and Africa. Greece shares land borders with ...
, built in the 6th century BC to serve as an aqueduct. The tunnel is the second known tunnel in history which was excavated from both ends (, "having two openings"), and the first with a geometry-based approach in doing so. Today it is a popular tourist attraction. The tunnel is inscribed on the
UNESCO The United Nations Educational, Scientific and Cultural Organization is a specialized agency of the United Nations (UN) aimed at promoting world peace and security through international cooperation in education, arts, sciences and culture. It ...
World Heritage List A World Heritage Site is a landmark or area with legal protection by an international convention administered by the UNESCO, United Nations Educational, Scientific and Cultural Organization (UNESCO). World Heritage Sites are designated by UNES ...
along with the nearby
Pythagoreion The Pythagoreion is the archaeological site of the ancient town of Samos in Samos, Greece. It is located in the area of the modern town of Pythagoreio, from which it has got its modern name. The archaeological site contains ancient Greek and Roma ...
and
Heraion of Samos The Heraion of Samos was a large sanctuary to the goddess Hera, on the island of Samos, Greece, 6 km southwest of the ancient city of Samos (modern Pythagoreion). It was located in the low, marshy basin of the Imbrasos river, near where it ...
, and it was designated as an International Historic Civil Engineering Landmark in 2017.


Early history

The Eupalinian aqueduct is described by
Herodotus Herodotus ( ; grc, , }; BC) was an ancient Greek historian and geographer from the Greek city of Halicarnassus, part of the Persian Empire (now Bodrum, Turkey) and a later citizen of Thurii in modern Calabria ( Italy). He is known f ...
(''Histories'' 3.60), without whom it might not have been discovered: :I have dwelt longer upon the history of the Samians than I should otherwise have done, because they are responsible for three of the greatest building and engineering feats in the Greek world: the first is a tunnel nearly a mile long, eight feet wide and eight feet high, driven clean through the base of a hill nine hundred feet in height. The whole length of it carries a second cutting thirty feet deep and three broad, along which water from an abundant source is led through pipes into the town. This was the work of a Megarian named Eupalinus, son of Naustrophus. The tunnel might also be referred to in the
Homeric Hymn The ''Homeric Hymns'' () are a collection of thirty-three anonymous ancient Greek hymns celebrating individual gods. The hymns are "Homeric" in the sense that they employ the same epic meter—dactylic hexameter—as the ''Iliad'' and ''Odyssey'', ...
to
Apollo Apollo, grc, Ἀπόλλωνος, Apóllōnos, label=genitive , ; , grc-dor, Ἀπέλλων, Apéllōn, ; grc, Ἀπείλων, Apeílōn, label=Arcadocypriot Greek, ; grc-aeo, Ἄπλουν, Áploun, la, Apollō, la, Apollinis, label= ...
, which mentions "watered Samos." The tunnel was dug in the mid-sixth century BC, by two groups working under the direction of the engineer
Eupalinos Eupalinos ( grc, Εὐπαλῖνος) or Eupalinus of Megara was an ancient Greek engineer who built the Tunnel of Eupalinos on Samos Island in the 6th century BC. The tunnel, presumably completed between 550 and 530 BC, is the second known tu ...
from
Megara Megara (; el, Μέγαρα, ) is a historic town and a municipality in West Attica, Greece. It lies in the northern section of the Isthmus of Corinth opposite the island of Salamis Island, Salamis, which belonged to Megara in archaic times, befo ...
, in order to supply the ancient capital of Samos (today called
Pythagoreion The Pythagoreion is the archaeological site of the ancient town of Samos in Samos, Greece. It is located in the area of the modern town of Pythagoreio, from which it has got its modern name. The archaeological site contains ancient Greek and Roma ...
) with fresh water. This was necessary for demographic reasons: the city of Samos had outgrown the capacity of the wells and cisterns within the city's limits, but the main source of fresh water on the island was on the other side of Mount Kastro from the city. It was of the utmost defensive importance; because the aqueduct ran underground, it could not easily be found by an enemy, who might otherwise cut off the water supply. The date of construction is not entirely clear. Herodotus mentions the tunnel in the context of his account of the tyrant
Polycrates Polycrates (; grc-gre, Πολυκράτης), son of Aeaces, was the tyrant of Samos from the 540s BC to 522 BC. He had a reputation as both a fierce warrior and an enlightened tyrant. Sources The main source for Polycrates' life and activit ...
, who ruled c. 540–522 BC, but he does not explicitly say that Polycrates was responsible for its construction. Aideen Carty suggests that it should be connected with the regime that overthrew the Geomori in the early sixth century BC, which granted citizenship to a large number of Megarians, perhaps including Eupalinos. The Eupalinian aqueduct was used as an aqueduct for 1100 years, before it began to silt up. In the seventh century AD, the south end was used as a defensive refuge.


Description


Spring and reservoir

The tunnel took water from an inland
spring Spring(s) may refer to: Common uses * Spring (season) Spring, also known as springtime, is one of the four temperate seasons, succeeding winter and preceding summer. There are various technical definitions of spring, but local usage of ...
, located about above sea level near the modern village of Ayiades. It discharges about 400 m3 of water per day. This spring was covered over. Two rectangular openings, each measuring , feed the water into a large reservoir with a roughly elliptical ground plan. Fifteen large stone pillars support a roof of massive stone slabs. The spring was thus completely concealed from enemies. The construction of this reservoir seems to have caused the outlet of the spring to subside by several metres. At some point before the nineteenth century, a church dedicated to St John was built over the top of this reservoir, further hiding the spring's location.


North channel

From the spring, a buried channel winds along the hillside to the northern tunnel mouth. The channel is long, although the distance from the spring to the tunnel mouth as the crow flies is only . The channel is wide and about deep. After it had been cut out of the bedrock, it was covered over with stone slabs and then buried. There are inspection shafts at regular intervals along the channel's course. The last of this channel pass under a small hill. Vertical shafts were dug from the surface at intervals of and then linked up to create a short tunnel, which brings the water.


Tunnel of Eupalinos

The tunnel through Mount Kastro carried the water for a distance of . The tunnel is generally . The southern half of the tunnel was dug to larger dimensions than the northern half, which in places is just wide enough for one person to squeeze through. The southern half, by contrast, benefits from being dug through a more stable rock stratum. In three sections, a pointed roof of stone slabs was installed to prevent rockfalls. Two of these sections, covering , are near the north end of the tunnel; the third section is m at the southern end of the tunnel. The walls of the tunnel were also faced with masonry in these sections, using polygonal masonry at the south end and large slabs at the northern end. In the
Roman Imperial period The Roman imperial period is the expansion of political and cultural influence of the Roman Empire. The period begins with the reign of Augustus (), and it is taken to end variously between the late 3rd and the late 4th century, with the beginning ...
,
barrel vault A barrel vault, also known as a tunnel vault, wagon vault or wagonhead vault, is an architectural element formed by the extrusion of a single curve (or pair of curves, in the case of a pointed barrel vault) along a given distance. The curves are ...
s were built with small stones and plaster to reinforce other sections of the tunnel. The width of the tunnel means that there would have been space for only two diggers to work at a time. To speed up the process, the tunnel was dug from both ends simultaneously. H. J. Kienast calculates that such workers would have been able to dig out of stone per day, meaning that the entire tunnel took at least eight years to dig. The floor of the tunnel is nearly horizontal and roughly above the level of the water at its source. Apparently, the subsidence at the spring lowered the level of the water after work had begun, leaving the tunnel too high. A separate channel had to be dug below the east half of the tunnel to carry the water itself. It increases in depth over the course of the tunnel, from m deep at the north end to at the southern end. Vertical shafts link this channel to the main tunnel roughly every ten metres. These were dug from the tunnel and then linked together to create the channel; once construction was finished, they served as inspection shafts. Debris from this channel was simply dumped in the main tunnel. A number of symbols and letters painted on the wall testify to a wide range of measurements. Three of them (Κ, Ε, and ΚΒ on the east wall), clearly mark the points where vertical shafts were cut. On the west wall, there are letters in alphabetical order at a regular interval of , which indicate that this was the basic unit of measurement used by Eupalinos (it is one fiftieth of the planned course through the mountain). The meanings of the other symbols have not yet been determined. Within the channel, the water was transported in a pipe made from terracotta sections, which were long and in diameter. The full pipe must have required around 5,000 of these sections. They were joined to one another with lime mortar. The top quarter of the pipes was cut open to allow sediment and other detritus to be removed, so that the aqueduct did not silt up. A break in the pipe near the north entrance of tunnel led to large amounts of mud entering the pipe, which had to be cleared out regularly. In the seventh century AD, when the aqueduct had ceased to operate, the southern section of the tunnel was converted to serve as refuge. This included the construction of a cistern from the southern entrance to collect water dripping from a vein in the rock.


Southern channel

Shortly before the southern mouth of the tunnel, the water channel diverges from the main tunnel and heads through the rock in a hidden channel like that to the north of the tunnel, which is buried just below the surface of the ground. It carries the water eastwards to the town of Pythagoreion. Only about of this channel have been excavated, but its total length must have been around . Two monumental fountains on the hillside inside the city seem to be on the line of this channel. They contained a reservoir and basins from which people could collect the water and carry it to their homes.


Surveying techniques and construction

In order to align the two tunnels, Eupalinos first constructed a "mountain line", running over the top of the mountain at the easiest part of the summit even though this gave a non-optimal position both for feeding water into the tunnel and for water delivery to the city. He connected a “south line” to the mountain line at the south side going straight into the mountain, which formed the south tunnel. At the north side a “north line” is connected to the mountain line, guiding the cut into the mountain from the north side. As the workers dug, they checked that their course remained straight by making sightings back towards the entrance of the tunnel. This is shown by a point in the southern half of the tunnel where the course accidentally diverged to the west and had to be corrected; a notch has been cut out of the rock on the inside of the curve, in order to restore the sight line. After from the northern end, an area full of water, weak rock and mud forced Eupalinos to modify his plan and direct the tunnel to the west. When leaving the line Eupalinos planned his diversion as an
isosceles In geometry, an isosceles triangle () is a triangle that has two sides of equal length. Sometimes it is specified as having ''exactly'' two sides of equal length, and sometimes as having ''at least'' two sides of equal length, the latter versio ...
triangle, with angles 22.5, 45, and 22.5 degrees. Measuring errors occurred and Eupalinos slightly overshot. When this was realised, the north tunnel was redirected to the east once more. The cutting of the south tunnel was completely straight, but stopped after . Eupalinos used a unit of for distance measurements and a unit of 7.5 degrees (1/12 of a right angle) for setting out directions.


Meeting point

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 (This method is documented by Hermann J. Kienast and other researchers). In planning the dig, Eupalinos used now well-known principles of
geometry Geometry (; ) is, with arithmetic, one of the oldest branches of mathematics. It is concerned with properties of space such as the distance, shape, size, and relative position of figures. A mathematician who works in the field of geometry is c ...
, codified by
Euclid Euclid (; grc-gre, Wikt:Εὐκλείδης, Εὐκλείδης; BC) was an ancient Greek mathematician active as a geometer and logician. Considered the "father of geometry", he is chiefly known for the ''Euclid's Elements, Elements'' trea ...
several centuries later. With a length of , the Eupalinian subterranean aqueduct is famous today as one of the masterpieces of ancient engineering. When the two tunnels reach within earshot, which can be estimated for this type of rock to approximate , the tunnels could be directed towards each other, but a high level of accuracy was required to reach that point. Errors in measurement and staking could cause Eupalinos to miss the meeting point of the two teams, either horizontally or vertically. He therefore employed the following techniques.


In the horizontal plane

Eupalinos calculated the expected position of the meeting point in the mountain. Since two parallel lines never meet, an error of more than horizontally meant that the north and south tunnels would never meet. Therefore, Eupalinos changed the direction of both tunnels, as shown in the picture (the north tunnel to the left and the south tunnel to the right). This gave a catching width that was wider by , so that a crossing point would be guaranteed, even if the tunnels were previously parallel and far away. They thus meet at nearly a right angle.


In the vertical plane

At the start of work, Eupalinos levelled around the mountain probably following a contour line in order to ensure that both tunnels were started at the same altitude. The possibility of vertical deviations in the process of excavation remained, however. He increased the possibility of the two tunnels meeting each other, by increasing the height of both tunnels at the point near the join. In the north tunnel he kept the floor horizontal and increased the height of the roof by , while in the south tunnel he kept the roof horizontal and lowered the level of the floor by . His precautions as to vertical deviation proved unnecessary, however, since measurements show that there was very little error. At the rendezvous, the closing error in altitude for the two tunnels was a few millimetres.


Rediscovery and excavation

Scholars began searching for the tunnel in the 19th century, inspired by the reference to it in Herodotus. The French archaeologist,
Victor Guérin Victor Guérin (15 September 1821 – 21 Septembe 1890) was a French intellectual, explorer and amateur archaeologist. He published books describing the geography, archeology and history of the areas he explored, which included Greece, Asia Mino ...
identified the spring that feeds the aqueduct in 1853 and the beginnings of the channel. In 1882, work began on clearing the tunnel with the goal of bringing it back into use. This proved too difficult and the effort was called off, but it allowed
Ernst Fabricius Ernst Christian Andreas Martin Fabricius (Darmstadt, 6 September 1857 – Freiburg im Breisgau, 22 March 1942) was a German historian, archaeologist and classical scholar. Between 1882 and 1888 he participated in excavations in Greece and Asia Mino ...
to investigate the tunnel on behalf of the
German Archaeological Institute The German Archaeological Institute (german: Deutsches Archäologisches Institut, ''DAI'') is a research institute in the field of archaeology (and other related fields). The DAI is a "federal agency" under the Federal Foreign Office of Germany ...
. He published the results in 1884 as "Die Wasserleitung des Eupalinos." Full excavations of the tunnel were carried out by Ulf Jantzen from 1971-1973, who finally cleared the full length of the tunnel, which had become filled with silt. A full survey of the tunnel with detailed
geodetic Geodesy ( ) is the Earth science of accurately measuring and understanding Earth's figure (geometric shape and size), orientation in space, and gravity. The field also incorporates studies of how these properties change over time and equivale ...
measurements was carried out by
Hermann J. Kienast Hermann or Herrmann may refer to: * Hermann (name), list of people with this name * Arminius, chieftain of the Germanic Cherusci tribe in the 1st century, known as Hermann in the German language * Éditions Hermann, French publisher * Hermann, Mis ...
. Portions of the tunnel are open to the public.


References


Literature

* * * * :* * * *


External links

* Olson, Åke: (2012). "How Eupalinos navigated his way through the mountain-An empirical approach to the geometry of Eupalinos"
Dan Hughes: The Tunnel of Eupalinos



The Tunnel of Eupalinos - Samos Explore

Tunnel of Eupalinos - Hellenic Ministry of Culture and Tourism

Tom M. Apostol: The Tunnel of Samos
{{DEFAULTSORT:Tunnel of Eupalinos Buildings and structures completed in the 6th century BC Aqueducts in Greece Ancient Greek buildings and structures Ancient Greek technology Ancient Samos Water tunnels Tunnels in Greece Historic Civil Engineering Landmarks