Conquest of Tunis ( 1535 ) The Conquest of Tunis in 1535 was an attack on Tunis , then under the control of the Ottoman Empire , by the Spanish Empire . Background . In 1533 , Suleiman the Magnificent ordered Hayreddin Barbarossa , whom he had summoned from Algiers , to build a large war fleet in the arsenal of Constantinople . Altogether 70 galley s were built during the winter of 1533 – 1534 , manned by slave oarsmen , including 2 , 000 Jewish ones . With this fleet , Barbarossa conducted aggressive raids along the coast of Italy , until he conquered Tunis on 16 August 1534 , ousting the local ruler , theretofore subservient to the Spanish , Muley Hasan . Barbarossa thus established a strong naval base in Tunis , which could be used for raids in the region , and on nearby Malta . Charles V , one of the most powerful men in Europe at the time , assembled a large army of some 30 , 000 soldiers , 74 galleys ( rowed by chained Protestants shipped in from Antwerp ) , 300 sailing ships , the " Santa Anna " and Portuguese galleon São João Baptista , also known as " Botafogo " and the most powerful ship in the world at the time , with 366 bronze cannons to drive the Ottomans from the region . The expense involved for Charles V was considerable , and at 1 , 000 , 000 ducats was on par with the cost of Charles ' campaign against Suleiman on the Danube . Unexpectedly , the funding of the conquest of Tunis came from the galleons sailing in from the New World , in the form of a 2 million gold ducats treasure extracted by Francisco Pizarro in exchange for his releasing of the Inca king Atahualpa ( whom he nevertheless executed on 29 August 1533 ) . Despite a request by Charles V , Francis I denied French support to the expedition , explaining that he was under a 3 year truce with Barbarossa following the 1533 Ottoman embassy to France . Francis I was also under negotiations with Suleiman the Magnificent for a combined attack on Charles V , following the 1534 Ottoman embassy to France . Francis I only agreed to the Pope Paul III ' s request that no fight between Christians occur during the time of the expedition . The battle . On 1 June 1535 , protected by a Genoese fleet , Charles V destroyed Barbarossa ' s fleet and , after a costly yet successful siege at La Goletta , captured Tunis . In the ruins , the Spanish found cannon balls with the French Fleur - de - lys mark , evidence of the contacts stemming from the Franco - Ottoman alliance . The resulting massacre of the city left an estimated 30 , 000 dead . Barbarossa managed to flee to Algiers with a troop of several thousands Turks . Muley Hasan was restored to his throne . The stench of the corpses was such that Charles V soon left Tunis and moved his camp to Radès . The siege demonstrated the power projection of the Habsburg dynasties at the time ; Charles V had under his control much of southern Italy , Sicily , Spain , the Americas , Austria , Netherlands and lands in Germany . Furthermore , he was Holy Roman Emperor and had " de jure " control over much of Germany as well . The catastrophic defeat in the Capture of Tunis in 1535 by the Holy League motivated the Ottoman Empire to enter into a formal alliance with France against the Habsburg Empire . Ambassador Jean de La Forêt was sent to Constantinople , and for the first time was able to become permanent ambassador at the Ottoman court and to negotiate treaties . Charles V celebrated a neo - classical triumph " over the infidel " at Rome on April 5 , 1536 in commemoration of his victory at Tunis . Aftermath . Barbarossa managed to escape to the harbour of Bône , where a fleet was waiting for him . From there , he sailed to accomplish the Sack of Mahon , where he took 6 , 000 slaves and brought them to Algiers . The Ottomans responded by recapturing the city in 1574 . However the Ottoman governors of Tunis were semi - autonomous Beyliks who acted as privateers against Christian shipping . Consequently , raiding in the Mediterranean continued until the French subjugated the region as a protectorate three centuries later in 1830 with an invasion leading to the creation of French Algeria , and the establishment of a Protectorate over Tunisia in 1881 through the French occupation of Tunisia .