The Ottomans knew Aydin Reis as Caccia Diavolo -- "Devil Hunter" -- a name that reflected both his reputation and the terror he inspired along the Spanish and Italian coasts. In 1529, he was operating from Algiers, recently conquered by the Ottoman-backed Barbary corsairs, raiding Christian shipping lanes and extracting Moriscos -- Muslims who had been forcibly converted to Christianity and now sought passage to North Africa. The Spanish armada was distracted, most of its strength committed to escorting Emperor Charles V to Genoa. Aydin exploited the gap, raiding Valencia and sacking settlements on Ibiza. But four Barbary fustas brought unwelcome news: the captain of the galley squadron of Granada had returned from Genoa and was hunting him with eight war galleys.

Desperate to avoid battle, Aydin dumped his non-combatants and cargo on Formentera and ordered his fleet to flee. The Spanish commander, Portuondo, gave chase with all the confidence of a man who held numerical parity in warships and superiority in galley type. But confidence undid him. His slave-powered galleys -- many crewed by recently captured French prisoners from the Italian Wars -- could not maintain a consistent pace. The Spanish ships strung out in a ragged line, with Portuondo's flagship pulling ahead of the rest. Aydin saw the gap open between the Spanish vessels and recognized the moment for what it was.

Aydin wheeled his three nearest ships around and fell on Portuondo's isolated flagship. The Spanish commander fought desperately, but outnumbered three to one and separated from his squadron, he was overwhelmed and killed in the defense. Aydin then turned on the rest of the scattered fleet, attacking each galley individually before it could close ranks with the others. The stunned Spanish crews, watching their commander's ship fall, offered resistance that crumbled ship by ship. By the time the engagement ended, seven of the eight Spanish galleys had been captured. Only one escaped. It was a textbook demonstration of how a numerically inferior force could defeat a larger one through tactical patience and an enemy's overconfidence.

The captured Spanish crews were taken as enslaved people to Algiers, joining the thousands already held in the corsair capital's dungeons and labor gangs. Portuondo's death created a vacancy at the head of the squadron of Granada, filled by Alvaro de Bazan the Elder, who would go on to become one of Spain's most celebrated naval commanders. The Battle of Formentera demonstrated how vulnerable Spanish Mediterranean shipping remained despite the empire's enormous resources. A single Ottoman corsair, operating from a recently captured port with improvised forces, had destroyed an entire galley squadron within sight of Spanish territory. The Balearic Islands, nominally safe waters for Spanish vessels, had proven anything but.