The Forts of Serra da Aguieira (Hills of Aguieira) were three forts constructed within 100 metres of each other as part of the second line of defence of the so-called Lines of Torres Vedras, which were constructed by Anglo-Portuguese forces in 1810 in order to protect the Portuguese capital Lisbon from possible invasion by the French during the Peninsular War.

The forts are situated in the municipality of Vila Franca de Xira, in the Lisbon District of Portugal.

In March 1809, Marshal Soult led a new French expedition that advanced south to the city of Porto before being repulsed by Portuguese-British troops and forced to withdraw.

[3] They were built at the top of the Aguieira mountain range, providing excellent views of the surrounding area and of the River Tagus.

[8] At an altitude of 274 metres the fort of Portela Grande was built as an irregular 11-sided polygon surrounded by a dry moat, with gun emplacements.