Fort in the shape of an undecagon. An earthwork, capped with stone.
It was part of the 2nd Line of the Lines of Torres Vedras. It covered the road between São Tiago dos Velhos and Casal da Portela, at the foot of Serra da Aguieira and Portela Pequena, as well as some points along the Alverca road between the abovementioned Casal, Romeira and the hill ascent.
It comprised a trench, an escarpment, a counterscarp, magazine, gun emplacements.
This fort was garrisoned by 350 infantrymen and equipped with 6 pieces of 12 calibre artillery.