Constructed in 1809–10, at 102 metres above sea level, it was one of the forts and other military works built by British and Portuguese troops to protect Lisbon from French forces, forming part of the Second Line of defence of the so-called Lines of Torres Vedras.

[1] The threat of invasion of Portugal by the French during the Peninsular War (1807–14) led to the construction of the Lines of Torres Vedras, to protect Lisbon from Napoléon Bonaparte's troops.

The defences were ordered by the British commander, the Duke of Wellington after two French invasions had already been repelled.

The fort was built on a hill, allowing it to defend the surrounding gorge and valley and the road from Ericeira to Sintra.

[2][3] Built into rock the stronghold of the fort has a hexagonal design and is surrounded by a moat.