The Fort of Cego is located in the municipality of Arruda dos Vinhos, in the Lisbon District of Portugal.

[1][2][3] Despite the defeat of French forces in earlier invasions of Portugal during the Peninsular War, the threat of further invasions led the commander of the British troops in Portugal, Arthur Wellesley, 1st Duke of Wellington, to order on October 20, 1809 the construction of defensive lines to the north of the capital, between the Atlantic Ocean and the River Tagus.

The Lines of Torres Vedras, consisting of 152 forts, redoubts and other military installations, were built rapidly and in great secrecy, under the overall supervision of Colonel Richard Fletcher who was commander of the Royal Engineers.

At 353 metres above sea level, it was on the first, or most northerly, of the three Lines of Torres Vedras, exchanging crossfire with the nearby Fort of Carvalha, with the aim of protecting the Arruda Valley.

It was originally named São Sebastião by the Portuguese Major Brandão de Sousa, but subsequently became known as the Fort of Cego.