It has a main span length of 1,013 metres (3,323 ft), making it the 48th longest suspension bridge in the world.

It is also commonly called the Tagus River Bridge (in Portuguese: Ponte sobre o Tejo, lit.

In the 1990s, a fifth car lane was added, and in 1999, a lower deck, used as a railway track, which was planned since the beginning, was finally built.

As a result, the Minister of Public Works, Duarte Pacheco, created a commission in 1933 to analyse the request.

Bids were obtained, but the proposal was subsequently put aside in favor of a bridge crossing the river at Vila Franca de Xira, 35 kilometres (22 mi) north of Lisbon.

In 1953, a new government commission started work and, in 1958, recommended building the bridge, choosing the southern anchor point adjacent to the recently-built Christ the King monument (Cristo-Rei).

In 1960, the winner was announced as a consortium headed by the United States Steel Export Company, which had also submitted a bid in 1935.

Also present were the Prime-Minister, António de Oliveira Salazar, and the Patriarch of Lisbon, Cardinal Manuel Gonçalves Cerejeira.

Morrison-Knudsen of Portugal Ltd., an American firm based in Boise, Idaho, was U.S. Steel's principal associate.

The bridge was designed by Steinman, Boynton, Gronquist and London of New York, and Tudor Engineering Company of San Francisco.

A symbol of those times was captured on film, with citizens removing the large brass letters spelling "Salazar" from one of the main pillars of the bridge and painting a provisional "25 de Abril" in its place.

Cars crossing the bridge make a peculiar hum - listen (59s) - because the two inner lanes are made of metallic grating rather than asphalt to minimize aerodynamic forces by means of pressure equalization.

However, the Government kept charging tolls well beyond the 20-year period, until it gave the concession to Lusoponte, creating a monopoly of the Tagus crossing in Lisbon.

When opened, people had to park their car and walk to buy a toll ticket costing 20 escudos.

As a result, a popular uprising led to road blockades of the bridge and consequent police charges, an event which made the right-wing Government highly unpopular and which many[who?]