The Tunnel of Samosf

7/27/2019 The Tunnel of Samosf

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30 E N G I N E E R I N G & S C I E N C E N O . 1

One of the greatest engineering achievements of ancient times is a water

tunnel, 1,036 meters (4,000 feet) long, excavated through a mountain on the

Greek island of Samos in the sixth century B.C.

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3E N G I N E E R I N G & S C I E N C E N O . 1

by Tom M. Apost ol

The Tunne l of Samos

One of the greatest engineering achievements ofancient times is a water tunnel, 1,036 meters(4,000 feet) long, excavated through a mountainon the Greek island of Samos in the sixth centuryB.C. It was dug through solid limestone by twoseparate teams advancing in a straight line fromboth ends, using only picks, hammers, and chisels.This was a prodigious feat of manual labor. Theintellectual feat of determining the direction oftunneling was equally impressive. How did theydo this? No one knows for sure, because no writtenrecords exist. When the tunnel was dug, theGreeks had no magnetic compass, no surveyinginstruments, no topographic maps, nor even muchwritten mathematics at their disposal. EuclidsElements, the first major compendium of ancientmathematics, was written some 200 years later.

There are, however, some convincing explana-tions, the oldest of which is based on a theoreticalmethod devised by Hero of Alexandria fivecenturies after the tunnel was completed. It callsfor a series of right-angled traverses around themountain beginning at one entrance of theproposed tunnel and ending at the other, main-taining a constant elevation, as suggested by thediagram below left. By measuring the netdistance traveled in each of two perpendiculardirections, the lengths of two legs of a righttriangle are determined, and the hypotenuse ofthe triangle is the proposed line of the tunnel.By laying out smaller similar right triangles at

each entrance, markers can be used by each crewto determine the direction for tunneling. Laterin this article I will apply Heros method to theterrain on Samos.

Heros plan was widely accepted for nearly2,000 years as the method used on Samos untiltwo British historians of science visited the site in1958, saw that the terrain would have made thismethod unfeasible, and suggested an alternativeof their own. In 1993, I visited Samos myself toinvestigate the pros and cons of these two methods

for aProject MATHEMATICS! video program,and realized that the engineering problem actuallyconsists of two parts. First, two entry points haveto be determined at the same elevation above sealevel; and second, the direction for tunnelingbetween these points must be established. I willdescribe possible solutions for each part; but first,some historical background.

Samos, just off the coast of Turkey in theAegean Sea, is the eighth largest Greek island,with an area of less than 200 square miles.Separated from Asia Minor by the narrow Straitof Mycale, it is a colorful island with lush vegeta-tion, beautiful bays and beaches, and an abun-dance of good spring water. Samos flourishedin the sixth century B.C. during the reign of thetyrant Polycrates (570522 B.C.), whose courtattracted poets, artists, musicians, philosophers,

and mathematicians from all over the Greekworld. His capital city, also named Samos, wassituated on the slopes of a mountain, later calledMount Castro, dominating a natural harbor andthe narrow strip of sea between Samos and AsiaMinor. The historian Herodotus, who lived inSamos in 457 B.C., described it as the mostfamous city of its time. Today, the site is partlyoccupied by the seaside village of Pythagorion,named in honor of Pythagoras, the mathematicianand philosopher who was born on Samos around

Facing page: This 1884

map by Ernst Fabricius

shows the tunnel running

obliquely through the hill

marked as Kastro, now

Mount Castro. The small

fishing village of Tigni has

since been renamed

Pythagorion. The cutaway

view through Mount Castro

at the top of this page

comes from a detailed

1995 survey by the

German Archaeological

Institute in Athens.

Below: Hero of

Alexandrias theoretical

method for working out

the line of a tunnel dug

simultaneously from both

ends.


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572 B.C. Pythagoras spent little of his adult lifein Samos, and there is no reason to believe that heplayed a role in designing the tunnel.

Polycrates had a stranglehold on all coastaltrade passing through the Strait of Mycale, andby 525 B.C., he was master of the eastern Aegean.His city was made virtually impregnable by a ringof fortifications that rose over the top of the 900-foot Mount Castro. The massive walls had anoverall length of 3.9 miles and are among thebest-preserved in Greece. To protect his shipsfrom the southeast wind, Polycrates built a hugebreakwater to form an artificial harbor. To honorHera, queen of the Olympian gods, he constructeda magnificent temple that was supported by 150columns, each more than 20 meters tall. And toprovide his city with a secure water supply, hecarved a tunnel, more than one kilometer long,

two meters wide, and two meters high, straightthrough the heart of Mount Castro.Delivering fresh water to growing populations

has been an ongoing problem since ancient times.There was a copious spring at a hamlet, nowknown as Agiades, in a fertile valley northwest ofthe city, but access to this was blocked by MountCastro. Water could have been brought aroundthe mountain by an aqueduct, as the Romanswere to do centuries later from a different source,but, aware of the dangers of having a watercourse

Clockwise from left: A well-preserved portion of the

massive ring of fortifications surrounding the ancient

capital; the impressive breakwater of Pythagorion; the

church in Agiades that now sits atop Eupalinoss colon-

naded reservoir; and a view of this tiny hamlet from the

south. (Agiades photos courtesy of Jean Doyen.)

exposed to an enemy for even part of its length,Polycrates ordered a delivery system that was tobe completely subterranean. He employed aremarkable Greek engineer, Eupalinos of Megara,who designed an ingenious system. The waterwas brought from its source at Agiades to thenorthern mouth of the tunnel by an undergroundconduit that followed an 850-meter sinuouscourse along the contours of the valley, passingunder three creek beds en route. Once inside thetunnel, whose floor was level, the water flowed ina sloping rectangular channel excavated along the

eastern edge of the floor. The water channel thenleft the tunnel a few meters north of the southernentrance and headed east in an undergroundconduit leading to the ancient city. As with thenorthern conduit, regular inspection shafts traceits path.

The tunnel of Samos was neither the first northe last to be excavated from both ends. Twoother famous examples are the much shorter, andvery sinuous, Tunnel of Hezekiah (also known asthe Siloam tunnel), excavated below Jerusalem


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around 700 B.C., and a much longer tunnel underthe English Channel completed in 1994. TheTunnel of Hezekiah required no mathematics atall (it probably followed the route of an under-ground watercourse), the Tunnel of Samos usedvery little mathematics, while the Channel Tunnelused the full power of modern technology. Thereis no written record naming the engineers forHezekiahs tunnel, just as there is none for thepyramids of Egypt, most cathedrals of Europe, or

most dams and bridges of the modern world.Eupalinos was the first hydraulic engineer whosename has been preserved. Armed only withintellectual tools, he pulled off one of the finestengineering achievements of ancient times. Noone knows exactly how he did it. But there areseveral possible explanations, and we begin withHeros method.

Hero, who lived in Roman Alexandria in thefirst century A.D., founded the first organizedschool of engineering and produced a technicalencyclopedia describing early inventions, togetherwith clever mathematical shortcuts. One ofhistorys most ingenious engineers and appliedmathematicians, Hero devised a theoreticalmethod for aligning a level tunnel to be drilledthrough a mountain from both ends. The contourmap on the right shows how his method could beapplied to the terrain on Samos. This map is partof a detailed, comprehensive 250-page reportpublished in 1995 by Hermann Kienast, of theGerman Archaeological Institute in Athens. Thesloping dashed line on the map shows the tunneldirection to be determined.

Using Heros method, start at a convenientpoint near the northern entrance of the tunnel,and traverse the western face of the mountainalong a piecewise rectangular path (indicated inred) at a constant elevation above sea level, untilreaching another convenient point near thesouthern entrance. Measure the total distancemoved west, then subtract it from the totaldistance moved east, to determine one leg of aright triangle, shown dashed on the map, whosehypotenuse is along the proposed line of thetunnel. Then add the lengths of the north-southsegments to calculate the length of the other leg,also shown dashed. Once the lengths of the twolegs are known, even though they are buriedbeneath the mountain, one can lay out smallerhorizontal right triangles on the terrain to the

north and to the south (shown in orange) havingthe same shape as the large triangle, with all threehypotenuses on the same line. Therefore, workerscan always look back to markers along this line tomake sure they are digging in the right direction.

This remarkably simple and straightforwardmethod has great appeal as a theoretical exercise.But to apply it in practice, two independenttasks need to be carried out with great accuracy:(a) maintain a constant elevation while goingaround the mountain; and (b) determine a right

This schematic diagram shows how Heros method can be

applied to the terrain on Samos. The hypotenuse of the

large right triangle is the line of the proposed tunnel.

Markers can be put along the hypotenuses of the small

right triangles at each entrance to help the tunnelers dig

in the right direction.

AGIADES

UNDERGROUND

CONDUIT

FORTIFICATIONS

NORTHERN

ENTRANCE

SOUTHERN

ENTRANCE

140

160

120

100

80

60

40

We can get an idea of

working conditions in the

tunnel from this Greek

mining scene depicted on a

tile found near Corinth.


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angle when changing directions. Hero suggestsdoing both with a dioptra, a primitive instrumentused for leveling and for measuring right angles.His explanation, including the use of the dioptra,was widely accepted for almost two millennia asthe method used by Eupalinos. It was publicizedby such distinguished science historians as B. L.van der Waerden and Giorgio de Santillana. Butbecause there is no evidence to indicate that thedioptra existed as early as the sixth century B.C.,

other scholars do not believe this method wasused by Eupalinos. To check the feasibility ofHeros method, we have to separate the problemsof right angles and leveling.

First, consider the problem of right angles. TheSamians of that era could construct right angles,as evidenced by the huge rectangular stones in thebeautifully preserved walls that extended nearlyfour miles around the ancient capital. Dozens ofright angles were also used in building the hugetemple of Hera just a few miles away. We dontknow exactly how they determined right angles,but possibly they constructed a portable rectangu-lar frame with diagonals of equal length to ensureperpendicularity at the corners. A carpenterssquare appears in a mural on a tomb at Thebes,dating from about 1450 B.C., so its reasonable toassume that the Samians had tools for constructingright angles, although the accuracy of these toolsis uncertain. In practice, each application of sucha tool (the dioptra included) necessarily introducesan error of at least 0.1 degree in the process ofphysically marking the terrain. The schematicdiagram on page 33 shows a level path with 28right angles that lines up perfectly on paper, butin practice would produce a total angular error ofat least two degrees. This would put the twocrews at least 30 meters apart at the proposedjunction. Even worse, several of these right angleswould have to be supported by pillars 10 metershigh to maintain constant elevation, which isunrealistic. A level path with pillars no morethan one meter high would require hundreds ofright angles, and would result in huge errors inalignment. Therefore, because of unavoidableerrors in marking right angles, Heros method isnot accurate enough to properly align the smallright triangles at the two entrances.

As for leveling, one of the architects of thetemple of Hera was a Samian named Theodoros,who invented a primitive but accurate leveling

instrument using water enclosed in a rectangularclay gutter. Beautifully designed round clay pipesfrom that era have been found in the undergroundconduit outside the tunnel, and open rectangularclay gutters in the water channel inside the tunnel.So the Samians had the capability to constructclay gutters for leveling, and they could haveused clay L-shaped pieces for joining the guttersat right angles, as suggested in the illustration onthe left. With an ample supply of limestone slabsavailable, and a few skilled stonemasons,

The southern entrance to the tunnel is somewhere within

the circle, in a grove of trees. The yellow line shows the

approximate route a straight path directly above the

tunnel would take over the south face of Mount Castro;

its a fairly easy climb.

Clay gutters like these

were found in the bottom

of the tunnels water

channel. They could have

been joined at right angles

by L-shaped pieces, and

used as leveling gutters

around the mountain.

Eupalinos could have marked the path with aseries of layered stone pillars capped by levelinggutters that maintained a constant elevation whilegoing around the mountain, thereby verifyingconstant elevation with considerable accuracy.

In 1958, and again in 1961, two Britishhistorians of science, June Goodfield and StephenToulmin, visited the tunnel to check the practica-bility of Heros theory. They studied the layout ofthe surrounding countryside and concluded that itwould have been extremely laboriousif notactually impossibleto carry out Heros methodalong the 55-meter contour line that joins the twoentrances, because of ravines and overhangs. Theyalso noticed that the tunnel was built under theonly part of the mountain that could be climbedeasily from the south, even though this placed itfurther from the city center, and they suggestedthat an alternative method had been used thatwent over the top, as shown in the photo above.

Armed with Goodfield and Toulmins analysis,I checked the feasibility of Heros method. Itstrue that the terrain following the 55-metercontour is quite rough, especially at the western

face of the mountain. But just a few metersbelow, near the 45-meter contour, the ground isfairly smooth, and it is easy to follow a goat trailthrough the brambles in a westerly directionaround the mountain. Eupalinos could havecleared a suitable path along this terrain andmarked it with stone pillars, keeping them ata constant elevation with clay leveling gutters,as described earlier, or with some other levelinginstrument. At the western end of the south face,the terrain gradually slopes down into a stream-


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Above: Mamikon

Mnatsakanian holds high

his invention, the leveling

bow, while Tom Apostol

(left) and our own Doug

Smith (right) check each

end. The diagram shows a

handheld lever that can be

used to stabilize the bowand fine-tune its elevation.

bed that is usually dry. An easy walk along thisstreambed leads to the northern face and a gentleslope up toward the northern entrance of thetunnel. Not only is the path around the moun-tain almost level near the 45-meter contour, it isalso quite shortfrom one tunnel entrance to theother is at most only 2,200 meters.

Goodfield and Toulmin suggested that the mostnatural way to establish a line of constant direc-tion would be along the top of the mountain,driving a line of posts into the ground up one faceof the hill, across the top, and down the other,aligning the posts by eye. To compare elevationson the two sides of the hill, they suggestedmeasuring the base of each post against thatimmediately below it, using a level. Thisapproach presents new problems. First, it isdifficult to drill holes in the rocky surface toinstall a large number of wooden posts. Second,aligning several hundred posts by eye on a hill-side is less accurate than Heros use of rightangles. Keeping track of differences in elevationis also very difficult. There is a greater chance oferror in measuring many changes in elevation

along the face of a hill than there would be insighting horizontally going around on a path ofconstant elevation. Because errors can accumulatewhen making a large number of measurements,Eupalinos must have realized that going overthe top with a line of posts would not give areliable comparison of altitude.

To ensure success, he knew it was essential forthe two crews to dig along a nearly level linejoining the two entrances. The completed tunnelshows that he did indeed establish such a line,

with a difference of only 60 centimeters inelevation at the junction of the north and southtunnels, so he must have used a leveling methodwith little margin for error. Water leveling withclay gutters, as described earlier, provides oneaccurate method, but there are other methodsthat are easier to carry out in practice.

Recently, my colleague Mamikon Mnatsakanianconceived an idea for another simple leveling toolthat could have been used, a long wooden bowsuspended by a rope from a central balancingpoint so that its ends are at the same horizontallevel. The bow need not have uniform thicknessand could be assembled by binding together twolengthy shoots from, say, an olive tree. Such abow, about eight meters long, would weigh aboutfour pounds and would be easy to carry. And ithas the advantage that no prior calibration is needed

To use the bow as a leveling tool, place it onthe ground and slowly lift it with the rope. If thetwo ends leave the ground simultaneously, theyare at the same elevation. If one end leaves theground first, place enough soil or flat rock beneaththat end until the other end becomes airborne. A

that instant, the bow will oscillate slightly, whichcan be detected visually, and the two ends will beat the same elevation. Three people are needed,one at the center and one at each end to fix thelevel points. To check the accuracy, turn the bowend-to-end and make sure both ends touch at thesame two marks. In this way, the device permitsself-checking and fine tuning. There will be anerror in leveling due to a tiny gap between theendpoint of the bow and the point on which it issupposed to rest when level; this can be checked


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BA

T

C

D

S

AGIADES

FORTIFICATIONS

140

160

120

100

80

60

180

40

N UNDERGROUNDCONDUIT

SOUTHERN

ENTRANCE

NORTHERN

ENTRANCE

by the human eye at close range, and would be oneor two millimeters per bow length.

To employ the leveling bow to traverse MountCastro at constant elevation, one can proceed asfollows. Construct two stone pillars, eight metersapart, and use the leveling bow to ensure that thetops of the pillars are at the same elevation. Atthe top of each pillar, a horizontal straightedgecan be used for visual sighting to locate otherpoints at the same elevation and on the samelinethe same principle as used for aimingalong the barrel of a rifle.

Points approximately at the same elevation canbe sighted visually at great distances. Choosesuch a target point and construct a new pillarthere with its top at the same elevation, and thenconstruct another pillar eight meters away tosight in a new direction, using the leveling bowto maintain constant elevation. Continuing inthis manner will produce a polygonal path ofconstant elevation. The contour map on the rightshows such a path in green, with only six changesin direction leading from point B near thenorthern entrance to pointD near the southernentrance. The distance around Mount Castroalong this path is less than 2,200 meters (275bow lengths), so an error of two millimeters perbow length could give a total leveling error ofabout 55 centimeters. This is close to the actual60-centimeter difference in floor elevationmeasured at the junction inside the tunnel.

In contrast to Heros method, no angular orlinear measurements are needed for levelingwith Mamikons bow.

Without Heros method, how could Eupalinoslocate the entry points and fix the direction fortunneling? Kienasts report offers no convincingtheory about this, but using information in thereport, Mamikon and I propose another methodthat could have determined both entries, and thedirection of the line between them, with consider-able accuraccy. Kienasts contour map (right)

By sighting horizontally along the tops of two pillars set

eight meters apart, a target point can be located up to

100 meters away; a possible error of two millimeters in

the elevations of the two pillars expands to an error of 25

millimeters in the elevation of the target point.

8 m

Using pillars and the leveling bow, a polygonal path, in green, can be traced around the

mountain at a constant elevation above sea level to join point Bnear the northern

entrance to point Dnear the southern.


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shows that the north entrance to the tunnel, pointA on the map, lies on the 55-meter contour line,and the source at Agiades is near the same contourline. His profile map in the report, which I haveadapted for the diagram above, reveals thatpersons standing at the crest of the mountaincannot see Agiades in the north and the seashorein the south at the same timebut they could ifthey were on top of a seven-meter-high tower atpoint T. The Samians could easily have con-structed such a tower from wood or stone.

Mamikon has conceived a sighting tool, basedon the same principle as the Roman groma, thatcould have been used to align Twith two points:one (N) near the source in the northern valley andone (S) on the seashore in the south within thecity walls. This sighting tool consists of a pair oftwo-meter-high fishing poles about five metersapart, with a thin string hanging vertically fromthe top of each pole to which a weight or plumb

bob has been attached. Each pole would bemounted on the tower so that it could turnaround a vertical axis, allowing the hangingstrings to be aligned by eye while aiming towarda person or marker at pointN. Sighting along thesame device in the opposite direction locatesS.

Using the same type of sighting instrumentfrom pointN, and sighting back toward T, thetunnels northern entrance (pointA) can be chosen

so thatS, T,N, andA are in the same verticalplane. Then the leveling bow can be used toensure thatA is also at the same elevation asN.

For the southern entrance, we need a point Cinside the city walls at exactly the same elevationasA. Starting from a nearby point B at a lowerelevation easier to traverse and in the verticalplane throughNandA, a series of sighting pillarscan be constructed around the western side of themountainusing any of the leveling methodsdescribed earlieruntil pointD, at the intersec-tion of the sighting plane through TandS, isreached. The two terminal points B andD willbe at the same elevation above sea level, and thevertical plane through points B, T, andD fixesthe line for tunneling. It is then a simple matterto sight a level line from the top of a pillar at Dto determine the southern entrance point, C, thathas the same elevation asA. Markers could beplaced along a horizontal line of sight at eachentrance to guide the direction of excavation.

How accurate is this method of alignment?In sighting from one fishing pole to its neighborfive meters away, there is an alignment error ofone millimeter, which expands to an overall errorof 22 centimeters in sighting from point Tat thetop of the mountain to pointN, 1,060 metersaway to the north, plus another error of 13centimeters from TtoS, 644 meters away to thesouth. So the total error in sighting fromNtoSby way ofTis of the order of 35 centimeters.

Adjusting this to account for the alignment errorfromNtoA by way ofB, and fromS to C by wayofD, gives a total error of the order of less than50 centimeters between the two directions oftunneling. This is well within the accuracyrequired to dig two shafts, each two meters wide,and have them meet, and is much more accuratethan the other proposed methods of alignment.Moreover, as with the alternative method ofleveling, no angular or linear measurementsare needed.

From a point seven meters

above the top of the

profile, there is a direct

line of sight to Agiades in

the north and the

seashore to the south. It

would have been easy for

Eupalinos to build a

surveying tower (T) there.

Two sighting poles such as

the ones shown below

could have been installed

on the tower to align with

markers Nand Sin Agiades

and on the shore,

respectively.

5 m

2 m

7 m


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This picture was taken inside the tunnel looking toward

the southern entrance. Although the floor is more or less

level along the whole length, the roof slopes in line with

the rock strata. Metal grillwork now covers the

water channel on the left to prevent hapless tourists

from falling in; the photo on the next page shows how

treacherous it was before.

The crew digging into the

northern mountainside

started off perfectly in line

with the southern crew,

but later zigzagged off

course, perhaps to bypass

areas of unstable rock.

They did, however, meet up

almost perfectly with the

southern tunnel, albeit at

right angles. Right: At the

southern end, the water

channel is a staggering

nine meters lower than the

floor of the tunnel.

A visit to the tunnel today reveals its fullmagnificence. Except for some minor irregulari-ties, the southern half is remarkably straight.The craftsmanship is truly impressive, both forits precision and its high quality. The tunnelstwo-meter height and width allowed workerscarrying rubble to pass those returning for more.The ceiling and walls are naked rock that givesthe appearance of having been peeled off in layers.Water drips through the ceiling in many placesand trickles down the walls, leaving a glossy,translucent coating of calcium carbonate, but someof the original chisel marks are still visible. Thefloor is remarkably level, which indicates thatEupalinos took great care to make sure the twoentrances were at the same elevation above sea level.

Of course, a level tunnel cannot be used todeliver a useful supply of water. The water itselfwas carried in a sloping, rectangular channelexcavated adjacent to the tunnel floor along its

eastern edge. Carving this innerchannel with hand labor in solidrock was another incredibleachievement, considering thefact that the walls of the channelare barely wide enough for oneperson to stand in. Yet they arecarved with great care, maintain-

ing a constant width throughout.At the northern end, the bottomof the channel is about threemeters lower than the tunnelfloor, and it gradually slopesdown to more than nine meterslower at the southern end. Thebottom of the channel was linedwith open-topped rectangularclay gutters like those in thedrawing on page 34.

No matter how it was planned, the tunnelexcavation itself was a remarkable accomplish-ment. Did the two crews meet as planned? Notquite. If the diggers had kept faith in geometryand continued along the straight-line paths onwhich they started, they would have made anearly perfect juncture. The path from the north,however, deviates from a straight line. When thenorthern crew was nearly halfway to the junctionpoint, they started to zigzag as shown in thediagram on the left, changing directions severaltimes before finally making a sharp left turn tothe junction point. Why did they change course?No one knows for sure. Perhaps to avoid thepossibility of digging two parallel shafts. If oneshaft zigzagged while the other continued in astraight line, intersection would be more likely.Or they may have detoured around places wherewater seeped in, or around pockets of soft materialthat would not support the ceiling. In the finalstretch, when the two crews were near enoughto begin hearing each other, both crews changeddirection as needed and came together. The sharpturns and the difference in floor levels at the junctionprove conclusively that the tunnel was excavatedfrom both ends. At the junction itself, the floorlevel drops 60 centimeters from north to south,a discrepancy of less than one-eighth of a percent

of the distance excavated. This represents anengineering achievement of the first magnitude.No one knows exactly how long it took to

complete the project, but estimates range from 8to 15 years. Working conditions during excava-tion must have been extremely unpleasant. Dustfrom rubble, and smoke from oil lamps used forillumination, would have presented seriousventilation problems, especially when the workershad advanced a considerable distance from eachentrance.


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Jane Apostol descends the dauntingly narrow wooden

staircase near the southern entrance, far left, which leadsto a narrow walled passageway whose gabled roof is typical

of ancient Greek construction, near left. Below: This old

photo of the tunnel, looking north, shows the open water

channel. Part of the channel above the water gutters was

originally filled in with rubble, some of which is still visible.

When the tunnel was rediscovered in the latterpart of the 19th century and partially restored,portions of the water channel were found to becovered with stone slabs, located two to threemeters above the bottom of the channel, ontowhich excess rubble from the excavation had beenplaced up to the tunnel floor. The generous spacebelow the slabs along the bottom of the channelprovided a conduit large enough for ample waterto flow through, and also permitted a person toenter for inspection or repairs. In several placesthe channel was completely exposed all the wayup to the tunnel floor, permitting inspectionwithout entering the channel. Today, most of therubble has been cleared from the southern half ofthe channel, and metal grillwork installed toprevent visitors from falling in.

To visit the tunnel today, you first enter a smallstone building erected in 1882 at the southernentrance. A narrow, rectangular opening in thefloor contains a steep flight of wooden stepsleading down into a walled passageway about 12meters long, slightly curved, and barely wideenough for one person to walk through. The sidesof the passageway are built of stone blocks joinedwithout mortar, and capped by a gabled roofformed by pairs of huge, flat stones leaningagainst each other in a manner characteristic of

ancient Greek construction. This passageway wasconstructed after the tunnel had been completelyexcavated. Excess rubble from the excavation, whichmust have been considerable, was used to cover theroof of this passageway, and a similar one at thenorth entrance, to camouflage them for protectionagainst enemies or unwelcome intruders. Electriclights now illuminate the southern half, up to apoint about 100 meters north of the junction withthe northern tunnel, where there is a barrier andlandfall that prohibits visitors from going further.


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Modern stone walls now line the path near the northern entrance of the tunnel, left, while

inside, right, a stone staircase leads down to the tunnel.

The videotape on the Tunnel of Samos has been a favoriteof the educationalProject MATHEMATICS! series(www.projectmathematics.com) created, directed, andproduced by Professor of Mathematics, Emeritus, TomApostol. He is, however, better known to students

both here and abroad as the author of textbooks incalculus, analysis, and number theory, books that havehad a strong influence on an entire generation ofmathematicians. After taking a BS (1944) and MS(1946) at the University of Washington, he moved toUC Berkeley for his PhD (1948), then spent a yeareach at Berkeley and MIT before joining Caltech in1950. Although he became emeritus in 1992, hismathematical productivity has not slowed downhehas published 40 papers since 1990, 16 of them jointlywith Mamikon Mnatsakanian.

For centuries, the tunnel kept its secret. Itsexistence was known, but for a long time theexact whereabouts remained undiscovered. Theearliest direct reference appears in the works ofHerodotus, written a full century after construc-tion was completed. Artifacts found in the tunnelindicate that the Romans had entered it, andthere is a small shrine near the center from theByzantine era (ca. A.D. 500900). In 1853,French archaeologist Victor Gurin excavated partof the northern end of the subterranean conduit,but stopped before reaching the tunnel itself. Anabbot from a nearby monastery later discoveredthe northern entrance and persuaded the ruler ofthe island to excavate it. In 1882, 50 menrestored the southern half of the tunnel, the entirenorthern underground conduit, and a portion ofthe southern conduit. On the foundation of anancient structure, they built a small stone housethat today marks the southern entrance. In 1883,Ernst Fabricius of the German ArchaeologicalInstitute in Athens surveyed the tunnel andpublished an excellent description, includingthe topographic sketch shown on page 30.

After that, the tunnel was again neglected fornearly a century, until the Greek governmentcleared the southern half, covered the waterchannel with protective grillwork, and installedlighting so tourists could visit it safely.

Today, the tunnel is indeed a popular touristattraction, and a paved road from Pythagorionleads to the stone building at the southernentrance. Some visitors who enter this buildinggo no further because they are intimidated by thesteep, narrow, and unlit wooden staircase leadingto the lower depths. At the north entrance,which can be reached by hiking around MountCastro from the south, modern stone walls leadto a staircase and passageway. A portion of thenorthern tunnel has been cleared, but not lighted.

The tunnel, the seawall protecting the harbor,and the nearby temple of Herathree out-standing engineering achievementswereconstructed more than 2,500 years ago. Today,the tunnel and seawall survive, and although thetemple lies in ruins, a single column still standsas a silent tribute to the spirit and ingenuity ofthe ancient Greeks.

This lone survivor is one

of 150 columns, each more

than 20 meters tall, that

once supported the Temple

of Hera, lauded by

Herodotus as one of the

three greatest engineering

feats of ancient times. The

other two were also on

Samosthe breakwater

and the tunnel.

PICTURE CREDITS: 30-31, 33, 36, 38 GermanArchaeological Institute;32-34, 38-40 TomApostol; 35 Bob Paz;39 Hellenic TAP Service

Documents

The Tunnel of Samosf