The French soon experience a reversal, however, at the hands of Peter III's admiral, Roger de Lauria.

The French fleet is defeated and destroyed at the Battle of Les Formigues on September 4, 1285 .There are three almost completely different accounts of this battle in Ramon Muntaner, Bernard Desclot, and the Gesta comitum Barchinonensium.

The Gesta places the battle at Les Formigues (or Formigas), while Muntaner favors a location off Roses (Rosas) to the north.

Either Lauria or the French are ashore for the night and encountered by the other, or they are both at sea when the encounter takes place.

The accounts agree that it happened at night, which was unusual for medieval naval battles, but suited Lauria, who is skilled at night-fighting.

He uses two lanterns on each galley to increase his apparent numbers.

Ten to sixteen Genoese galleys under John de Orreo flee, leaving about fifteen to twenty French galleys to be captured, and some others sunk or burnt, which destroys for a long time the French naval power in the Mediterranean.

The troubadour Joan Esteve blames treachery for the capture of the French admiral Guilhem.

It is said that three hundred French prisoners were sent back to France.

All of the prisoners but one had their eyes gouged out, and that one was left with one eye to guide the others.

The prisoners brought one message from Roger of Lauria to the King of France: that not even fish would be able to navigate safely through Mediterranean Sea without a shield or sign of the king of Aragon on them.