The Aqueduct of Free Waters is one of the most remarkable examples of 18th century Portuguese engineering. Its main course covers 18 km, but the whole network of canals extends through nearly 58 km.

The city of Lisbon has always suffered from the lack of drinking water, and King John V decided to build an aqueduct (started in 1731) to bring water from sources in Caneças. In 1748, although the project was still unfinished, the aqueduct started to bring water to Lisbon.