Wellington took refuge behind the Lines of Torres Vedras

After Bussaco, Wellington took refuge behind the Lines of Torres Vedras, which were in fact three lines north of Lisbon (the third one being around the temporary port at Oeiras), which had been built at speed and in secrecy, overseen by Col. Richard Fletcher (1768-1813), a Royal Engineer. The 152 forts were manned by Portuguese militia and ordenanças, leaving the regular troops to intervene when needed. Massena has no idea of the existence of these Lines. After spending the winter before them with increasing problems of supplies he retired first to Santarém, and then left Portugal in March, 1811. The Tagus was defended by the Royal Navy gunboats.

For more information, please see:

The Lines of Torres Vedras: A Remarkable Restoration Project

The Lure of the Lines - The Confession of a Lines Junkie