This issue commemorates the opening of the Aqueduct of the Free Waters in 1748, after 12 years of construction, to bring more drinking water into Lisbon – the water from the river Tagus is salty. The aqueduct and reservoir system was extended until 1834 and deactivated in 1967. It is considered one of the masterpieces of Baroque engineering.
The main part of the aqueduct is 14km long, from the Free Waters source in Belas to the Mother of Water reservoir in Amoreiras, but the whole system is 58km long, with 47km of canals collecting water from 58 sources, and 11km distributing it within Lisbon. The miniature sheet shows the main and subsidiary aqueducts in the region of Amadora and Queluz, nowadays heavily populated suburbs of Lisbon.
The most visible part of the aqueduct are the 35 arches spanning 941m over the valley of Alcântara, including the largest ogival arch in the world, with a height of 65m and a span of 29m. Major motorways and a railroad now pass under the arches, quite a different scenery from the stamp’s picture… Completed in 1744, this part of the aqueduct resisted the 1755 earthquake and can nowadays be visited: there is a pathway along the waterway above the arches, so that residents could walk from Monsanto over the valley into Lisbon. During 1836-9 many people fell from the aqueduct. The authorities first thought it was a wave of suicides, but it became clear it was murder and the pathway was eventually closed. The culprit was caught after murdering a family during a house burglary, and he was sentenced to death and hanged in 1841. His head was subject to medical study and is still preserved at the Museum of Medicine.
On a more peaceful note, in 2005 I chaired the European Software Engineering Conference, which took place on the central campus of the New University of Lisbon, in Campolide, overlooking the aqueduct. I commissioned the conference logo to be a stylised image of it.
The stamp was designed by Carlos Leitão, lithographed by the Mint on enamelled paper sheets with perforation 12×12½, and circulated from 20 February 1998 to 30 September 2001.