The British retreat across the Peninsular stopped at the prepared positions in the lines of Torres Vedras. Massena's cavalry made their first contact on the 11 October. Massena viewed the lines on the 14th October and realised he could not attack so formidable defence. He held position before the lines for four weeks occasionally probing and skirmishing before retreating twenty five miles on the 14th November because local foraging could no longer sustain his army. Massena had lost a significant number of men to hardship and starvation. With few shots fired and no battle being fought Wellington had won a significant victory. On the 6th March 1811 Massena began a full retreat.

Defensive lines to the North and North East of Lisbon, Portugal. The lines followed the best defensive ground running roughly in a North West [anchored on the coast] to South East [anchored on the Tagus] direction. (Portugal)

Wellington recognized that the most important element in the battle for Portugal was the possession of Lisbon and the control of the Tagus. To defend these he gave orders on the 20th October 1809 to his chief engineer to build a great line of fortresses, namely the Lines of Torres Vedras.
Massena was given command of the Army of Portugal in May 1810