The huge Roman aqueduct built in Segovia, Spain, by the Roman Emperor Trajan (AD 98-117).
One of the best preserved Roman engineering works, the structure was constructed from approximately 24,000 dark colored Guadarrama granite blocks without the use of mortar. The above ground part is 2,388 feet long. And it consists of approximately 165 arches that are more than 30 feet in height.
Mark Beré Peterson: Hauntings, Urban Legends, History, Folklore, Mythology and Witchcraft 