The combat of Guarda (14 April 1812) was Marmont's only significant success during his belated attempt to help the defenders of Badajoz, and came eight days after the city had fallen to Wellington's men.
At the start of 1812 Marmont had been unable to react in time to stop Wellington seizing Ciudad Rodrigo, and orders from Napoleon then prevented him from doing anything effective to help the defenders of Badajoz, after Wellington moved south to attack that city for the third time.
When Marmont did finally move, it was into an area that didn’t concern Wellington at all. He advanced south-west towards Sabugal, across the Portuguese border, but a position that didn't threaten any of Wellington's depots, or his control of the key fortresses at Almeida or Ciudad Rodrigo.
Two divisions of Portuguese militia, under Generals Trant and Wilson, were moved to Guarda, to the north-west of Sabugal, to watch Marmont. Marmont reached Sabugal on 8 April, and then sent out columns which raided the surrounding area, and briefly captured the magazines at Castello Branco.
Trant and Wilson came up with a plan to attack Marmont while his forces were scattered, but they moved too slowly. Marmont had learnt that they were only twenty miles away, and decided to lead 7,000 men to attack them - five squadrons and light cavalry and a brigade each from Sarrut's and Maucune's divisions.
At dawn on 14 April Marmont and his cavalry had reached the foot of the steep hill of Guarda, without being detected by the militia. However he then paused to allow the infantry to catch up, and this gave the militia time to realise how much danger they were in. Trant and Wilson ordered their men to retreat, and they managed to get safely out of the town, although in some disorder.
Marmont decided to send his cavalry to try and catch the retreating militiamen. Trant's men were caught at the bridge of Faya, three miles to the west/ north-west of Guarda, where the road crossed the Mondego River. The militiamen were caught entirely by surprise and the division fell apart. Around 1,500 men were cut off, although the French only bothered taking around 500 prisoners, allowing the others to disperse. Wilson's men had got across the river, and the French cavalry decided not to risk attacking a larger force across a narrow bridge.
On the following day news of the fall of Badajoz reached Marmont, along with a report that Wellington was already moving north. Marmont withdrew from Guarda to Sabugal, where he reformed his scattered units. He then withdraw back into Spain, although only after coming close to being caught by Wellington. On 22-23 April Marmont finally retreated, using a series of fords near Ciudad Rodrigo to cross the Agueda River. From there he retreated east towards Salamanca, and his most famous defeat.