Short answers, pulled from the story.
Divisional-General Pierre Dupont de l'Étang commanded the French forces during the Battle of Bailén. He led a corps of 13,000 men consisting primarily of second-line troops originally raised for internal police services or garrison duty in Prussia.
The main fighting occurred between the 16th and the 19th of July 1808 over three bloody days. General Reding crossed the river at Mengíbar on this timeline to seize Bailén and interpose himself between the two wings of the French army.
A total of 17,000 men were captured when Dupont agreed to surrender his own forces and Vedel's division. This figure represents the worst defeat suffered by the French in the entire Peninsular War.
The Spanish transferred 7,000 prisoners to the uninhabited island of Cabrera because they could barely supply their own armies in the field. The rank and file prisoners were also sent to the Canary and Balearic Islands where inhabitants protested at their proximity.
Dupont was court-martialed, deprived of rank and title, and imprisoned at Fort de Joux upon returning to Paris. He was not paroled until the restoration of Louis XVIII with rumors persisting that he had been quietly assassinated in captivity.