On the Cover: Roman Aqueduct at Segovia, Spain

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The ancient aqueduct at Segovia, Spain is one of the most significant and best-preserved monuments of the Roman occupation of the Iberian Peninsula. While the date of construction is unknown (the original inscription would have been on the now-missing attic, or top section), researchers believe it was constructed between the second half of the first century CE and the early years of the second, during the reign of either emperor Vespasian or Nerva. The aqueduct transports waters from Spring Fuenfría, situated in the nearby mountains 10.6 miles from the city. Water first collects in a tank known as El Caserón (big house), before being led through a channel to a second tower known as the Casa de Aguas (waterhouse), where it is naturally decanted before continuing on its route. Water then travels nearly a half-mile on a 1% grade until it enters the Postigo, a rocky outcropping upon which the old city center, the Segovia Alcázar, was built. Then, at Plaza de Díaz Sanz, the structure makes an abrupt turn and heads toward Plaza Azoguejo (shown), where it displays its full splendor. At its tallest, the aqueduct reaches a height of 93.5 feet, including nearly 20 feet of foundation; the pillars support both single and double arches. From the point at which it enters the city until it reaches Plaza de Díaz Sanz, the aque-duct consists of 75 single arches and 44 double (there are 167 arches in total). The construction of the Segovia aqueduct followed the principles established by Vitruvius in his De Architectura, published in the latter half of the first century BCE. The Roman engineers built the structure with brick-like granite blocks placed without mortar. During the Roman era, each of the three tallest arches displayed a sign in bronze letters, indicating the name of its builder along with the date of construction. Today, two niches are still visible, one on each side of the aqueduct. One of them is known to have held the image of the Egyptian Hercules, who according to legend was the founder of the city; the other niche now contains the statues of the Virgen de la Fuencisla (the Patroness of Segovia) and Saint Stephen.

During the reign of King Ferdinand and Queen Isabella (1474–1516), 36 arches of the aqueduct were rebuilt, with great care taken not to change the original work or style. Later, during the sixteenth century, the central niches and statues were placed on the structure. Today, the aqueduct is the city's most important architectural landmark. It had been kept functioning throughout the centuries and preserved in excellent condition. Until recently, it still provided water to Segovia, mainly to the Segovia Alcázar. In addition to the natural erosion of the granite itself, during recent decades the structure has been affected by pollution, especially from vehicular traffic, which until recently passed through its arches. Restoration projects have been ongoing since 1997 in order to ensure the aqueduct's survival; vehicular traffic has been rerouted, and Plaza Azoguejo has been converted into a pedestrian mall.

This aqueduct is a fitting symbol of the mission of CTTS. The hydraulic and construction technologies represented in this structure and mastered by Roman engineers were "lost" for centuries after the demise of the Roman empire. Yet both the structure itself and the entire water system it was part of continued to function throughout the centuries. The inability of later generations to replicate such projects until the modern era demonstrates how even possession of a particular technology does not guarantee the ability to master its technical "secrets." Observers could rather easily discern how the system worked, but not emulate or copy it. The knowledge of a working system includes not only the codified knowledge of science and engineers, but also the skills and more tacit forms of knowledge that enable craftsmen and -women to actually carry out the design. Thus even the reintroduction of Vitruvius to European readers was not enough to allow the construction of similar projects. Absent both knowledge and skills, as well as the cultural capacity to...