The monumental arches spanning the Alcântara Valley are the hallmark of the Águas Livres Aqueduct, designated a National Monument since 1910, but they represent only a small fraction of the entire network. At 941 meters long, the series of arches accounts for about 1.6% of a system that—including the main aqueduct, branches, and distribution pipes—spanned approximately 58 kilometers by the mid-19th century.
Construction of this project began in 1731. To finance the project, the “Real d’Água” was established—a tax levied on goods purchased at the time, notably olive oil, meat, and wine. The main canal was inaugurated in 1748, but the system’s construction was not fully completed until 1799.
The world’s largest stone arch
The visible section of the aqueduct stands out for its pointed arches. One of these arches holds the title of the world’s largest stone arch, rising to a height of 65 meters. The entire infrastructure was designed to operate solely and exclusively by the force of gravity.
The system was fed by 60 springs. From there, water was distributed through five tunnels, which carried the water to about 30 fountains scattered throughout the city.
Resilience to the 1755 Earthquake
The soundness of the engineering behind the Águas Livres Aqueduct was put to the test just a few years after its inauguration. When the great earthquake of 1755 struck and destroyed much of the capital, the aqueduct’s structure remained standing.
Its survival of the earthquake attested to the quality of its construction, leaving intact what has become one of the most striking pieces of infrastructure in the city’s landscape.
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