As they approached Lisbon after the battle of Bussaco and their sacking of Coimbra, the French plan was simple enough. They would sweep everything before them as they had previously, except that next time they met the Anglo-Portuguese troops would not have a strong defensive position from which to maul the French army as at Bussaco. Thus, although shaken by their experience at Bussaco, the French were confident that the British troops would have no choice but to embark on their ships and leave Lisbon. Perhaps here and there a strong redoubt might have to be besieged but, in the long run, Lisbon would fall.
General of Division Michel Clarapède (1772–1842). Clarapède led a division of the 9th Corps which was heavily engaged at Fuentes de Oñoro on 5 May 1811.
Once the formidable Lines of Torres Vedras were reached, the plan for the leisurely capture of Lisbon vaporised. Masséna and his generals had no inkling of the existence of these fortifications and had never planned for anything of the sort. The probe at Sobral and other skirmishes confirmed the extraordinary strength and extent of this network. From then on, there was no French plan, only increasingly desperate improvisation in a worsening situation. Thus was the retreat of the starving army to Santarem brought about, and thus the retreat to the Spanish border. While it might be argued that the battle of Fuentes de Oñoro occurred because Masséna wanted to maintain a foothold in Portugal to allow a later invasion, this was more wishful thinking than a genuine plan.
General of Division Louis-Pierre Montbrun (1770–1812), commander of the cavalry reserve of Masséna’s army.
The aim of the British and the Portuguese was to inflict as much damage as possible on the French invasion army while keeping their own fighting capacity as intact as possible. Even while Wellington’s Anglo-Portuguese army was fighting to delay the French in the north, the country mobilised to build the Lines of Torres Vedras according to Wellington’s far-sighted defence plan of the autumn of 1809. When the French eventually reached the lines it would require considerable efforts to pierce the defences. Another part of the plan was a ‘scorched earth’ policy by the Portuguese to leave as little as possible to the French troops, who were used to living off the land. In the event, the French army could not ultimately sustain itself before the Lines and had to retreat to Santarem to survive. The next step would be for Wellington’s Allied army to pursue them to Spain and, if the opportunity arose, to bring on a general engagement – an opportunity that would come at the small dusty village of Fuentes de Oñoro.