For centuries, nobody knew exactly when the aqueduct was built. The bronze letters that once spelled out the builder's name and the construction date were long gone, leaving only the anchor holes in the stone. In the late twentieth century, the epigrapher Geza Alfoldy studied those anchor patterns and determined that Emperor Domitian likely ordered the construction, proposing 98 AD as the completion date. Then, in 2016, archaeologists published evidence pointing to a slightly later date -- after 112 AD, during the reign of Trajan or possibly the early years of Hadrian. The aqueduct predates certainty about its own origins, which seems fitting for a structure that has outlived every government that ever claimed it.

The system begins at the Rio Frio, 17 kilometers away in the mountains of the La Acebeda region. Water was first gathered in a collection tank called El Caseron, then channeled to a second structure, the Casa de Aguas, where sand and sediment settled out naturally. From there, it traveled 728 meters on a gentle one-percent grade toward the rocky promontory where Segovia's walled old city sits, crowned by its Alcazar. The engineering follows principles laid out by Vitruvius in De Architectura, published in the mid-first century BC -- a textbook the builders apparently knew well. At Plaza Azoguejo, where the aqueduct reaches its full height, the double-tiered arches create a procession of stone that manages to be both monumental and elegant, each pillar tapering slightly from a base of 2.4 by 3 meters to a top cross-section of 1.8 by 2.5 meters.

The Moors destroyed 36 arches in 1072. Four centuries later, during the reign of Ferdinand and Isabella, the prior of the nearby Jeronimos del Parral monastery led a painstaking reconstruction, rebuilding every one of those arches while taking great care to match the original style. In the sixteenth century, niches were added to the structure -- one once held an image of Hercules, the legendary founder of Segovia, now replaced by the Virgin Mary. Cadets from the local military academy still drape the image of the Virgen de la Fuencisla in a flag each December 4, the feast day of Saint Barbara, patron saint of artillery. The aqueduct's granite blocks, unmortared and precisely cut, held together through gravity and geometry alone for all those centuries.

When the water finally stopped flowing in 1973, the aqueduct's second life as a pure monument began -- though in some ways it had always been one. Segovia's old town and the aqueduct together received UNESCO World Heritage status in 1985. But time and pollution have taken their toll. Differential stone decay, water leakage, and cracking in the granite ashlar prompted the World Monuments Fund to list the site on its 2006 Watch. A collaboration between Spain's Ministry of Culture, the regional government of Castilla y Leon, and WMF Spain, supported by American Express, launched conservation efforts. Today, one of Segovia's former mint buildings -- the Real Casa de Moneda -- houses an interpretation center dedicated to the aqueduct, funded by European Economic Area grants. Stand beneath the arches at Plaza Azoguejo and look up: the blocks fit together with the precision of a puzzle, each one holding its neighbor in place through sheer engineering conviction, as they have for nearly two thousand years.