The Unsigned Survey (the original Tunnel of Eupalinos story)

Sometimes surveyors make mistakes, but while the blunders of other professionals such as doctors are soon dead and buried, ours tend to acquire immortality. Also, unlike doctors, surveyors like to talk about the shortcomings of their peers, or to write about them.

Sometime around 530 B.C., when Polycrates was tyrant of the Greek island of Samos, a need arose to build an aqueduct. The water was to be carried by a clay pipe, and the pipe laid in a trench of constant grade, with just enough of a slope to keep the water flowing. A hill about 900 feet high stood in the way of the project and the engineer, a fellow by the name of Eupalinus of Megara, decided to pierce the hill by driving a tunnel through it. Impatient, Polycrates apparently was rushing the project along, and Eupalinus, reasoning that he could cut the construction time in half, decided to start digging the tunnel from opposite ends. To clear the hill, a 3,300-foot tunnel had to be chiseled through solid rock. To give sufficient elbow room to the workers, a height and width of about 5.5 feet was decided upon. Inside that cross section, a trench was to be dug for the water pipe.

The Greek historian Herodotus considered this tunnel one of the three greatest engineering works of the Greek world, and when he wrote about it he exaggerated its length to make sure his readers were impressed. He did not say how the survey was done or what instruments were used, but he did not have to. Anyone can appreciate the problem. As they approach each other, the two opposing adits must meet, because if they don’t you will end up with two tunnels.

For more than 2,000 years, engineers employed a simple but expensive method to control the direction and elevation of tunneling operations. At regular intervals of about 150 feet, a vertical shaft was dug from the tunnel to the surface, allowing the engineer to look around and determine where he was. A variation of that method was employed as late as 1871 in Cincinnati, where pipes were driven from the tunnel to the surface above. But to raise shafts in a tunnel that is 900 feet below the surface, more digging would have to be done in the shafts than in the tunnel itself.

Eupalinus apparently trusted that any surveyor would have the knowledge required to assure that the two adits would meet in the middle of the hill. By 500 B.C., plenty of tunnels had been dug, and the surveying devices as well as the geometry available to the surveyors more than justified his trust. It was, however, just as easy to pick a bad surveyor as it was to pick a good one, as it still is today. Eupalinus may well have checked prices and decided to go with the low bidder. What is in a survey anyhow?

And so the miracle developed. Whenarchaeologists investigatedabout 100 years ago, they found that the surveyors had messed the thing up. The tunnelers had missed each other by 20 feet in the horizontal and three feet in the vertical, way too much of an error in alignment for the technology of the time.

We do not know of course whether Eupalinus deserved better. After all, he could consider himself lucky. Chiseling in solid rock, the workers could hear each other hammering over a distance of 20 feet and make the correction, even if they could not prevent the resulting kink in the tunnel. But Eupalinus probably could not help screaming when he learned that the relatively small vertical error was deceptive. The elevation of the tunnel was all wrong. To maintain the grade, the trench holding the water pipe, which was already an excessive eight feet deep at the upstream entrance, had to be dug 28 feet deep at the downstream exit of the tunnel, an indication of a pretty good boo-boo during the leveling operation or in the determination of the elevations on both ends prior to the tunneling.

One must assume that Eupalinus had better luck in the selection of his public relations man. To praise the project as one of the greatest on the island of Samos and beyond and to maintain that illusion until the late 1800s was quite an accomplishment. As for the surveyor? There is no record of any surveyor having been demoted to the quarry gang, and whoever he was, he smart enough not to have chiseled his name into the walls of the tunnel. Also, as far as is known, nobody mentioned the tunnel survey as a reference on any job application.

As even the layman should know, sooner or later botched surveys will cost somebody a lot of money. The Samos tunnel was no exception. It may be coincidence, but we do know that Polycrates ran out of money and turned to piracy until he was caught and crucified in 522 B.C.

About the Author

Fred Roeder, LS

Fred Roeder lives in Tularosa, New Mexico. He emigrated to the United States from Germany in 1957 and spent most of his surveying career in the Southwest, working for the U.S. Forest Service. Now retired, he started writing a regular column for the New Mexico Professional Surveyors Newsletter in 1988. In 1994, NMPS produced Antepasados, a book of his columns. Many surveyors are good writers, especially about technical or legal matters. However, it's not often that we find a surveyor/story-teller who can present historical facts in a manner that makes them fun to read. Fred Roeder is such a writer and we are pleased to present more than 80 of his stories here. Bibliography is a list of the books Fred used in his writings, and includes a numbered index of the articles. Index is a list of all the articles Fred has written and when. Editor's pick: The King Who Had No Title
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