The discovery of Brazilian gold in 1697 led to a new wave of prosperity for Portugal and Lisbon. From 1706, King Joao V began an ambitious building program in the city. The most valuable addition to Lisbon at this time was the Aguas Livres Aqueduct which, started in 1732, was carrying water across the Alcantara valley by 1748. The main pipeline measures 12 miles (19 km) but the total length, including all secondary channels, is 36 miles (58 km). The most visible part of this imposing and grandiose structure are the 35 arches that cross the Alcantara valley, the tallest of which rise to a spectacular 213 feet (65 m) above the ground.
This aqueduct also served as a pedestrian walkway, a very pleasant promenade, until closed in 1853 following a series of crimes committed from its lofty structure. Diogo Alves, an infamous robber of the time, would throw his victims over the edge from its heights. The aqueduct runs from Belas, north of Lisbon, via its many arches across the Alcantara valley to the Mae das Aguas reservoir, near the Largo do Rato in western Lisbon. The aqueduct includes a total of 109 arches across the valley and remained in use from 1748 until 1967.