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Modern Description: The left branch of the road continues 300m further west to the most interesting and significant site of the city, the aqueduct of Eupalinos (open daily except Monday 8.25 am - 2.45 pm), worthy of visit not just because it is a 1,036m long, double-tunnel, cut by hand through the mountain—itself a remarkable feat, but nonetheless achievable in the 6th century BC by means of the power of captive, or slave, labour—but because of what it tells us about the rapid evolution of Greek thinking at that time. The fact that the tunnel was begun simultaneously from two points (invisible to one another) on opposite sides of a mountain and met in the centre at a depth of 170m below the surface, with almost negligible margin of error, is an incarnation of the Greeks' extraordinary and evolving ability to solve problems by the application of logic and theoretical imagination to practical situations. The quantity (17 cubic metres per hour) and quality of water rising year-round at the spring of Aghiades, 2.5km, as the crow flies, behind the mountain to the north of the city, made it the obvious source for Samos, which was fast growing into one of the largest cities in the Aegean in the 6th century BC. The water from the spring could have been channeled around the slopes of the hill and brought into the city from the west. But the fact that this was not done, and that the much more difficult task of bringing it directly through the mountain was chosen instead, indicates that an external aqueduct was possibly considered too vulnerable to attack by an enemy.
Archaeological evidence (potsherds, and the style of masonry in the areas of reinforcement), as well as the testimony of Herodotus, suggest that the tunnel could well have been commissioned by Polycrates, in the same period as the first circuit of walls and the harbour mole(s), i.e after 540 BC—even though some important authorities (notably the archaeologist, Hermann Kienast) put the start of the tunnel around ten years earlier, before the rule of Polycrates. The nature of the threat to Samos was apparently urgent enough to necessitate the bold decision to begin the tunnel from both ends simultaneously, so as to halve the time to completion. It was with that decision that the most interesting problems were raised. Herodotus gives the name of the engineer as Eupalinos, son of Naustrophos, from the city of Megara, between Athens and Corinth. ‘Eupalinos' is suspiciously similar to the epithet ‘eupalamos', meaning ‘ingenious', ‘inventive' or ‘skillful', and may possibly be a sobriquet given to the architect after the completion of his remarkable works. Eupalinos had to construct the tunnel on a perfect horizontal. To cut it on a gradient ran the risk of the tunnel flooding and becoming unworkable, if a seam of flowing water were accidentally to be encountered during the digging. The last, and unpredictable, kind of problem he faced—areas of unstable rock, which threatened collapse— does appear to have been encountered by Eupalinos, some way in from the north entrance. It was so bad that it forced him to deviate from a straight line in search of a more stable area to cut through. This had serious consequences for him, because it inevitably meant that the sightline from the cutting-face to the daylight at the entrance was lost for good, as soon as he deviated. Thereafter, he was literally and metaphorically working in the dark. In correcting his initial deviation, once good rock was again found, he appears to have overcompensated and lost the correct alignment. There was always a risk that the two troops would miss and continue oblivious of one another; now the risk was even greater. To ensure that this did not happen, he devised a simple solution: the trajectory of both campaigns was turned slightly to the same (east) side, so that if the level of each tunnel really were identical, sooner or later they had to cross one another's path; which they did. It is this manoeuvre that accounts for the irregularity of line in the middle of the tunnel. A passage was now open right through the heart of the mountain.
Once the two sections of the tunnel were successfully joined, three further works remained. First of all, a channel now had to be excavated with the necessary gradient to allow the water to flow constantly. This was first done to one side of the floor of the tunnel; but it appears that, due to what Kienast sees as a lowering of the level of the spring, a subsidiary tunnel had to be dug below the existing one, at a substantially lower level. This was created by sinking broad shafts down from the side of the floor, approximately every 12m, and connecting them below into a continuous sloping waterway; the southern exit is about 4.7m lower than the northern entrance, representing a gradient of 1:220. This lower tunnel was then lined with terracotta ducts for the water. Next the water had to be brought in a superficial, but hidden, aqueduct from the spring at Aghiades to the north entrance of the tunnel.
Finally another aqueduct had to link the southern exit to cisterns and the network of pipes and fountains across the inhabited area of the city. This runs parallel to the hillside and is sunk below ground; the regular shafts used for its construction are visible beside (mostly below, but latterly above) the road which leads to the site.
The two vertical shafts for fixing the direction of the south section of the tunnel can be seen from outside where they sink into the ground— one between the ticket booth and the entrance; the other, just above the entrance building. Of the two, only the second is visible inside the tunnel, at the end of the first stretch of narrow passageway after the steps. Standing in the pool of light it casts, you can see down the length of the tunnel. The sides of the tunnel have a slightly serpentine irregularity, due simply to human error in cutting; but any deviation is always corrected and the axial line remains perfectly straight. The entrance was modified after the original opening became dangerous due to surface erosion; this is why the site is now entered by steps from above, and it means that the daylight from its entrance can no longer be seen from inside. At the foot of the steps you pass through a narrow section between the beautifully constructed, Archaic strengthening walls, made in large polygonal blocks, and capped with a pointed ceiling.
The body of the tunnel is roughly square in section, on average measuring 180 x 180cm. The limestone walls and ceiling are heavily indented with the striations of the pick. As you proceed down the tunnel, on the right hand side are the regular shafts which drop down to the lower tunnel which was connected in both directions from the base of each shaft to form a continuous passage; the waste stone was cleared out through the shaft, and some of it used to fill in the original water-channel which was now not in service. On the floor of the lower tunnel were the water pipes—composed of about 5,000 individual segments, interlocking, and sealed together. Hard to detect, but just visible in places, close to the floor on the east wall, are the engineer's marks: these are mostly level lines, used to indicate the depth of the trench. Beyond the area that is accessible to visitors, are a couple of inscriptions sketched in red paint; one is a name, ‘Asbideo', another reads ‘Parade[i]gma' (‘plan'). The illuminated and accessible sector of the tunnel ends after approximately 250m: rock-fall has now closed the central section. On leaving the site, the exit of the lower tunnel which carried the water pipes—at this point, 8m below the upper tunnel—can be seen to the west side below the steps that lead out of the fenced area.
The north end of the tunnel presents different aspects of interest. (This can be reached by foot (50 mins.), directly across the hill-top over which the line of the tunnel was originally traced by Eupalinos; the entrance is low down on the south side of a declivity to your left as you descend into an area of pine-trees. The spring is 15 mins. further to the north/northwest. Alternatively, it may be reached by the road which branches left at the exit of Pythagóreio on the road to Vathý, climbs past the ancient walls, and drops over a brow into the broad valley of the Aghiades spring. The church and spring are found 800m along the road which branches left at the first T-junction. To find the tunnel entrance from the spring: walk back east along the road until there is a rough track bearing to the right, which soon begins to climb steeply up to the right to a crossing of tracks by some pine-trees.
The right-hand track from here descends into the dip, on the south side of which is the north entrance of the tunnel, somewhat hidden in undergrowth.) The spring of Aghiades, whose abundant waters were the cause of the tunnel building, rises beneath the church of Aghios Ioannis, beside the road in the village of Aghiades. A fragment of a carved, Byzantine templon is set in a niche above the church's west door. The church is built directly over the ancient spring-house and cistern, whose roof—now the church's floor—is supported by a forest of square, marble pillars. The water level in the cistern today is lower than in Antiquity, and the water is ducted directly to Pythagóreio.
Immediately to the south side of the church can be seen the beginning of the closed channel which bore the water from here to the entrance of Eupalinos's tunnel. A hole in its roof at one point allows the interior to be seen; originally the whole structure was hidden just below ground level for security. The channel follows the contours of the hill first towards the south, and then making a deep dogleg east before sharply returning west again, reaches the tunnel entrance after 900m. Shafts (whose openings are often hidden and unprotected) used for the construction of the channel can be located in the course of the last 300m. The north entrance (currently accessible, though work appears to be beginning on fitting a new gate: torch or flashlight necessary) has been restored in the last 25 years, but below and to the right is the ‘dromos' of the original entrance.
Wikipedia: https://en.wikipedia.org/wiki/Tunnel_of_Eupalinos
Wikidata ID: Q955894

Info: McGilchrist's Greek Islands

(From McGilchrist’s Greek Islands, © Nigel McGilchrist 2010, excerpted with his gracious permission. Click for the books)

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