A Brief History of the Lines of Torres Vedras
The Lines of Torres Vedras were build to defend the Portuguese Capital City, Lisbon during the Peninsular War. The allied army under the Duke of Wellington needed a secure base where he could resist if the French concentrated their larger forces against him. There was nowhere else in Portugal where Wellington believed he could win.
The Duke ordered their construction in October 1809 and they were ready to use in October 1810 when the Allied army arrived followed by the invading French army under Marshal Massena.
The French realised the Lines were too strong and remained in front of them until March 1811, when starvation left them with no altenative to retreat.
The French never again approached the Lines, but they remained a safe point for the Allied army for the remainder of the war.
The Portuguese nation suffered terribly to achieve this victory. All civilians in front of the Lines were ordered to abandon their homes and destroy anything that would be useful to the French. Tens of thousands of Portuguese civilians died during the winter of 1810 as they waited behind the Lines for the French to retreat