Fuentes de Oñoro was the final battle in the third French invasion of Portugal. I highly recommend David Buttery's Wellington Against Massena for a full history of the invasion.
The British under Wellington, then Wellesley, had successfully driven out two previous French invasions of Portugal, Junot's in 1808 and Soult's in 1809, before Massena undertook the third in May 1810. The invasion route drove straight towards Lisbon with the French successfully taking the forts of Ciudad Rodrigo and Almeida as they began their advance. The British retreated before them until they came to Bussaco ridge where, in what became a classic example of a Wellington battle, the French columns having made the difficult climb were repulsed by the British and Portuguese lines before there could fully reform.
The battle, whilst a defeat, did not prevent the invasion continuing as the British again fell back. While it may have seemed that the campaign would end with the British being driven into the Atlantic, on the 11 October 1810 the advanced French cavalry came across Wellington's masterstroke. Began a year previously based on Wellington's initial assessment of the strategic situation the Lines of Torres Vedras were the undoing of Massena's army. Unable to penetrate the works and with his army struggling on low supplies Massena was forced to retreat in early 1811.
As the British pursued Napoleon decided that Massena, previously one of his greatest Marshals, was no longer up to the task and Marmont was dispatched to assume command. Having being pursued past the fort of Almeida which the British now besieged, Massena decided on one last throw of the dice to try and defeat Wellington in open battle.
In early May 1811 the British had advanced as far as the town of Fuentes de Oñoro on the Portuguese-Spanish border just past Almeida, and it was here that Massena decided to attack. Wellington had around 34,000 infantry and 2,000 cavalry compared to Massena's 44,000 infantry and 4,500 cavalry. The British did however outnumber the French in artillery with 48 guns to the 38 guns of the French. Massena was also being undermined by Marshal Bessières. Massena had already fallen out with Marshal Ney who had returned to France. Bessières was in command of the Army of the North and although he had brought some supplies and 1,600 cavalry to support Massena, he was reluctant to follow Massena's orders.
The battlefield centred on the town of Fuentes de Oñoro with the river Dos Casas running north-south presenting the first obstacle the French would have to cross. The fort of Almeida, which Massena hope to relieve lay to the north west of Fuentes de Oñoro behind the battlefield. The British held the slopes running down from Almeida to the Dos Casas north of Fuentes. While this might have been a more natural route to avoid Fuentes, the terrain either side of the Dos Casas was difficult leaving an attacker exposed to the enemy on the far side.
The 3 May 1811 saw the first French attacks on Fuentes with their initial success stopped by the arrival of British reinforcements. Realising that Fuentes was well defended Massena spent the 4th probing the British position looking for weak points before deciding on an attack plan for the 5th. The plan was straight forward, Reynier's Corps would provide a diversionary attack north of Fuentes while d'Erlon's Corps would attack Fuentes itself. With the British pinned the remaining French forces, including most of the cavalry, will advance south of Fuentes turning the British right.
Wellington had played into this plan. His forces were spread over a wide area and on his right the 7th Division, newly arrived in the Peninsular, was positioned at Poco Velho detached from any supporting Divisions.
So we have the scenario. Will the French be able to turn the British right and roll-up the line? Will Wellington send reinforcements to support and extract the 7th Division and redress his line?
The scenario is played using the forces given in the Grande Armée rule book, I have however added to the map provided which I find to be a little bare. The main changes being to add additional hills to give a better feel of the landscape and to add rough terrain to represent the ravine north of Fuentes, otherwise it is too easy for the French to attack the Britsh here.