A stratagem adopted by Wellington at the crucial early stage of his Peninsular campaign. In autumn 1809 he reconnoitred the area between Lisbon, Torres Vedras, the Atlantic coast, and the river Tagus accompanied by Col Richard Fletcher, his chief engineer. He had been forced out of Spain, and wished to site field fortifications to help him to hold Lisbon if the French followed up. The positions were constructed over the next year. Forts and batteries on hills commanded all likely approaches, with lengths of rampart between them to impede enemy advance. Semaphore towers enabled the defenders to communicate. There were three lines: the first, running for 29 miles (47 km) through Torres Vedras itself, between the Tagus at Alhandra and the coast south of the Ziandre estuary; the second, rather stronger line some 6 miles (9.7 km) to the south; the third, centred on Fort St Julian on the Tagus estuary, secured an embarkation beach in case all else failed. The first line proved to be sufficient.
Wellington withdrew into the Lines in October 1810. The French commander Masséna had no knowledge of them, and could neither attack them nor supply his army if it remained before them. He soon fell back about 30 miles (48 km), but his men grew increasingly hungry, and terrorized the inhabitants in their quest for food. In March 1811 Masséna retreated at last, and Wellington pursued. The character of the war had changed. With Portugal secure, Wellington was now free to attack ‘the keys of Spain’, the fortresses of Badajoz and Ciudad Rodrigo.
— Richard Holmes
