From the 1880s onwards, the Alviela River became Lisbon’s main drinking water supplier (a situation that remained until the mid-20th century). To transport the water gravimetrically, a gigantic aqueduct of more than 100 km in length (the largest aqueduct in Portugal and the oldest still in operation) was built between the river source and the city. In some places, the aqueduct is underground; in others, it is on the surface.

When it needs to cross a valley, it rises above an arcade, like the Louriceira Aqueduct, with 18 arches. Built in limestone, the water flows inside a closed channel at the top of the aqueduct. A few days ago, on a beautiful late afternoon, I saw the sunset through one of the aqueduct arches. On the horizon, the silhouette of a large stone pine stood out.

Some birds of prey hovered in the sky, certainly waiting to detect a prey—a rabbit or a mouse—that they could capture. Scattered clouds in beautiful pink colours completed the landscape.