The Aqueduct

About fifty miles northwest of Madrid and near the western slopes of the Sierra de Guadarrama lies the ancient city of Segovia. The town nestles on a 300 feet high rocky spur between the confluence of two rivers, its medieval walls rising proudly out of a canyon, and its late Gothic cathedral piercing the blue sky of Old Castile. For several centuries it was a favorite residence of the Castilian kings who left their mark on the enchanting castle that is gracefully perched on the westernmost apex of the rock, overlooking the mingling waters of the rivers below.

The city is blessed with an abundance of architectural marvels, but its pride is its magnificent Roman aqueduct. The aqueduct was built sometime in the first century A.D., probably during the reign of Trajan, and for nearly two millennia its sharp silhouette has dominated the view of the city and been its coat-of-arms. Until just a few years ago, when it was cut to yield to the demand of modern traffic, it brought water from the nearby mountains to the thirsty city.

For most of its ten mile length the water was channeled at or below the ground, but the last half mile, where the aqueduct crosses a valley that separates the old town from the surrounding plateau, it required an elevated structure of stone arches. There are 167 of them; including 88 double ones (arch on top of arch) that rise to a maximum height of ninety-three feet. The visitor gazes in disbelief as he discovers, that except for the lofty water channel the entire structure was built without mortar or clamps, its integrity depending entirely on the marvelous skills of the stone masons who stacked the huge boulders on top of each other and fitted them together. Two thousand years of often turbulent history have weathered and rounded the granite, but failed to as much as nudge the massive yet graceful arches.

Building an extraordinary aqueduct like the one in Segovia required the services of a competent and experienced surveyor. Profoundly impressed by this imposing sight, my mind drifted back through the centuries to imagine that proud Roman surveyor, wondering who he might have been and what his days were like, as he struggled with the clumsy level and the awkward numerical system of his time.

If water is to flow in a narrow open channel by the action of gravity alone, a fairly constant grade is very important. The slope must be sufficient for a steady flow, but not as steep as to allow the water to spill over the sides in the curves or at the inlets of the distribution pipes, a shallow drop of something like two or three feet per mile would be about right.

The planning stage requires a carefully surveyed ground profile between the source and the final destination. After construction has begun, a surveying error would be extremely difficult to correct, requiring a major change in design or dooming the entire project. The Romans were not noted for gracefully accepting apologies.

The modern surveyor, with bureaucrats meddling, lawyers looking over his shoulder, and malpractice insurance rates on the rise, might be tempted to long for the “good old days”. May this story serve as a reminder that excellence in the performance of our profession is at least as old as the splendid aqueduct at Segovia.