"The Lines of Torres Vedras were lines of forts built in secrecy to defend Lisbon during the Peninsular War. Named after the nearby town of Torres Vedras, they were ordered by Arthur Wellesley, Viscount Wellington, constructed by Sir Richard Fletcher, 1st Baronet, and his Portuguese workers between November 1809 and September 1810, and used to stop Masséna's 1810 offensive.

The lines were divided up into districts by Wellington in letter dated 6 October 1810:

From Torres Vedras to the sea. HQ at Torres Vedras
From Sobral de Monte Agraço to the valley of Calhandrix. HQ at Sobral de Monte Agraço
From Alhandra to the valley of Calhandrix. HQ at Alhandra
From the banks of the Tagus, near Alverca, to the Pass of Bucellas, inclusive. HQ at Bucellas
From the Pass of Freixal, near Bucellas, inclusive, to the right of the Pass of Mafra. HQ at Montachique
From the Pass of Mafra to the sea. HQ at Mafra
Each district was allocated one Captain and one Lieutenant of Engineers.

The total number of troops to Wellington's hand for the defence of the entire position amounted, exclusive of two battalions of marines in the lines round São Julião, to 42,000 British, of whom 35,000 were effective; in addition to which he had over 27,000 Portuguese regulars, of whom 24,000 were effective; about 12,000 Portuguese militia; and 20–30,000 of the ordenanças, which last were of little value except for guerilla warfare. Lastly, the Marquis of la Romana with great generosity brought 8,000 Spaniards of his division likewise within the lines about Mafra. Altogether, therefore, Wellington had some 60,000 regular troops whom he could depend upon, and 20,000 more who could be trusted at least to fight behind earthworks.

The redoubts of the first line did not require more than 20,000 men to defend them, which left the whole of the true field-army free not only to reinforce any threatened point but also to make a counter-attack. To facilitate such movements a chain of signal-stations had been formed from end to end of the lines, and lateral roads of communication had been made so as to enable the troops to pass rapidly along their entire length.

Wellington did not abuse his fortified position by distributing his troops, according to the vicious cordon-system, in small fractions along the entire front, but kept his field-army for the most part in two masses on the centre and right, so that the whole could be assembled in a few hours."