Designed in 1746 by the Hungarian architect Carlos Mardel, this reservoir was built to receive and distribute the water carried by the Águas Livres Aqueduct.

Inside the building this reservoir stands out with a depth of 7.5 meters. At the top it is possible to access the panoramic terrace overlooking the city of Lisbon.

On the western front of the reservoir is the Register House, where water flows driven to fountains, factories, convents and noble houses were controlled. Classified, since 1910, as a National Monument.