The document discusses the Tunnel of Eupalinos, an ancient aqueduct tunnel on the Greek island of Samos built in the 6th century BC. The 1,036 meter tunnel was engineered by Eupalinos to transport water from an inland spring to the town of Pythagoreion. Eupalinos used innovative geometric techniques to ensure the two tunneling teams would meet in the middle, including changing the tunnels' directions and adjusting their heights. Today the tunnel remains an impressive feat of engineering and is a popular tourist attraction.

1. Erasmus+ 2016-2017
Team: Greece
Anna Kotsa – Irene Avgerinou

2.  The Tunnel of Eupalinos or Eupalinian aqueduct is
a tunnel of 1,036 m (3,399 ft) length in the island
of Samos, Greece.
 It was built in the 6th century BC to serve as
an aqueduct (a tunnel constructed to convey water).
 The leading engineer was Eupalinos, after whom the
tunnel took its name.
 The tunnel is the second known tunnel in history
which was excavated from both ends.
 It is the first tunnel with a geometry-based approach
of construction.
 Today it is a popular tourist attraction.

3. The location of Samos in Greece The inside of the tunnel of Eupalinos

4.  The tunnel took water from an inland spring, which
was roofed over and thus concealed from enemies.
 A buried channel winds along the hillside to the
northern tunnel mouth.
 A similar hidden channel, buried just below the
surface of the ground, leads from the southern exit
eastwards to the town of Pythagoreion (the capital city
of the ancient Sam0s).

7.  In the mountain itself, the water used to flow in pipes
in a separate channel several meters below the human
access channel, connected to it by shafts or by a
trench.
 The southern half of the tunnel was dug to larger
dimensions than the northern half and has a pointed
roof of stone slabs to prevent rock falls. The southern
half, by contrast, benefits from being dug through a
more stable rock stratum.

9.  In order to make the two halves of the tunnel meet in
the middle of the mountain, Eupalinos used what are
now well-known principles of geometry.
 Eupalinos was aware that error 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:

10. In the horizontal plane
Since two parallel lines never meet, Eupalinos
recognized that an error of more than two meters
(6.6 ft) horizontally would make him miss the meeting
point. Having calculated the expected position of the
meeting point, 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 from each other.

11. In the vertical plane
Similarly, there was a possibility of deviations in the
vertical sense, even though his measurements were
quite accurate. However, 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 in the vertical sense proved
unnecessary, since measurements show that there was
very little error.

12. Here is a short video about the tunnel of Eupalinos:
Video of Tunnel of Eupalinos
Movie of Tunnel of Eupalinos