Barbarossa had left Algiers in 1535 to be named High Admiral of the Ottoman Empire in Constantinople, and was replaced as governor by Hasan Agha, a Sardinian eunuch and renegade.

[3] A fleet led by Andrea Doria was dispatched with the help of allied nations including the Republic of Genoa, the Kingdom of Naples, and the Order of Saint John of Jerusalem to transport the troops from Spain and the Netherlands.

[18] Distinguished Spanish commanders accompanied Charles V on this expedition, including Hernán Cortés, the conqueror of Mexico, though he was never invited to the War Council.

[16] German, Spanish, and Italian troops, accompanied by 150 Knights of Malta, began to land while repelling Algerine opposition, soon surrounding the city, except for the northern part.

[3] Hayreddin's deputy Hassan Agha had a strong defence at the gate of Bab Azzoun and caused serious casualties among the Maltese knights.

[21] Andrea Doria managed to find a safer harbour for the remainder of the fleet at Cape Matifu, five miles east of Algiers.

This elusive "one thing" is never stated; however Charles Lamb suggests that Shakespeare drew upon the legend of an unnamed Algerian witch who summoned a ferocious tempest which destroyed the 1541 invasion fleet, and it was this act of defending her nation which prevented her people from executing her.