Siege of Nice The Siege of Nice occurred in 1543 and was part of the Italian War of 1542 – 46 in which Francis I and Suleiman the Magnificent collaborated in a Franco - Ottoman alliance against the Holy Roman Emperor Charles V , and Henry VIII of England . At that time , Nice was under the control of Charles III , Duke of Savoy , an ally of Charles V . This is part of the 1543 - 1544 Mediterranean campaign of Barbarossa . The siege . In the Mediterranean , active naval collaboration took place between France and the Ottoman Empire to fight against Spanish forces , following a request by Francis I , conveyed by Antoine Escalin des Aimars . The French forces , led by François de Bourbon , and the Ottoman forces , led by Hayreddin Barbarossa , first joined at Marseilles in August 1543 . Although the Duchy of Savoy , of which Nice was a part , had been a French protectorate for a century , Francis I chose to attack the city of Nice with the allied force , mainly because Charles III , Duke of Savoy had angered him by marrying Beatrice of Portugal , thus becoming an ally of the Habsburgs . François de Bourbon had already attempted to make a surprise attack on Nice once , but had been repulsed by Andrea Doria . Arrival of the Ottoman fleet . Following an agreement between Francis I and Suleyman the Magnificent , through the intervention of the French ambassador in Constantinople Polin , a fleet of 110 galleys under Hayreddin Barbarossa left from the Sea of Marmara in mid - May 1543 . He then raided the coasts of Sicilia and Southern Italy through the month of June , anchoring in front of Rome at the mouth of the Tiber on June 29 , while Polin wrote reinsurances that attacks against Rome would not take place . Barbarossa arrived with his fleet , accompanied by the French Ambassador Polin , at Île Saint - Honorat on July 5 . As almost nothing had been prepared on the French side to assist the Ottoman fleet , Polin was dispatched to meet with Francis I at Marolles and ask him for support . Meanwhile , Barbarossa went to the harbour of Toulon on July 10 , and then was received with honours at the harbour of Marseilles on July 21 , where he joined the French forces under the Governor of Marseille , François , Count of Enghien . The combined fleet sailed out of Marseille on the 5th of August . Siege . The Ottoman force first landed at Villefranche , 6 kilometers east of Nice , which it took and destroyed . The French and Ottoman forces then collaborated to attack the city of Nice on 6 August 1543 . In this action 110 Ottoman galleys combined with 50 French ones . The Franco - Ottomans were confronted by a stiff resistance which gave rise to the story of Catherine Ségurane , culminating with a major battle on 15 August , but the city surrendered on 22 August . The French prevented the Ottomans from sacking the city . They could not however take the castle , the " Château de Cimiez " , apparently because the French were unable to supply sufficient gunpowder to their Ottoman allies . Another important battle against the castle took place on 8 September , but the force finally retreated upon learning that an Imperial army was on the move to meet them : Duke Charles III , ruler of the Duchy of Savoy , had raised an army in Piedmont to free the city . The last night before leaving , Barbarossa plundered the city , burned parts of it , and took 5 , 000 captives . The relief army , transported on ships by Andrea Doria , landed at Villefranche , and successfully made its way to the Nice citadel . During the campaign , Barbarossa is known to have complained about the state of the French ships and the inappropriateness of their equipment and stores . He famously said " Are you seamen to fill your casks with wine rather than powder ? " . He nevertheless displayed great reluctance to attack Andrea Doria when the latter was put in difficulty after landing the relief army , losing 4 galleys in a storm . It has been suggested that there was some tacit agreement between Barbarossa and Doria on this occasion . Catherine Ségurane . Catherine Ségurane ( " Catarina Ségurana " in the Niçard dialect of Provençal ) is a folk heroine of the city of Nice , France who is said to have played a decisive role in repelling the city ' s siege by Turkish invaders allied with Francis I , the Siege of Nice , in the summer of 1543 . At the time , Nice was part of Savoy , independent from France , and had no standing military to defend it . Most versions of the tale have Catherine Ségurane , a common washerwoman , leading the townspeople into battle . Legend has it that she knocked out a standard bearer with her beater and took his flag . However , according to one commonly told story , Catherine took the lead in defending the city by standing before the invading forces and exposing her bare bottom . This is said to have so repulsed the Turkish infantry ' s Muslim sense of decency that they turned and fled . However , in Turkish culture , the practice of " mooning " is considered odd or absurdly immoral but never offensive and most probably as a sexual teasing , especially when performed by a female . Catherine ' s existence has never been definitively proven , and her heroic act of mooning is likely pure fiction or highly exaggerated ; Jean Badat , a historian who stood witness to the siege , made no mention of her involvement in the defense . Historically attested defense of Nice include the townspeople ' s destruction of a key bridge and the arrival of an army mustered by a Savoyard duke , Charles III . Nevertheless , the legend of Catherine Ségurane has excited the local imagination . Louis Andrioli wrote an epic poem about her in 1808 , and a play dedicated to her story was written by Jean - Baptiste Toselli in 1878 . In 1923 , a bas - relief monument to Catherine was erected near the supposed location of her feat . In Nice , Catherine Segurane Day is celebrated annually , concurrent with St . Catherine ' s Day on November 25 . Ottoman wintering in Toulon . Following the siege , the Ottomans were offered by Francis to winter at Toulon , so that they could continue to harass the Holy Roman Empire , and especially the coast of Spain and Italy , as well the communications between the two countries . Barbarossa was also promised that he would receive help from the French in reconquering Tunis if he stayed through the winter in France . Throughout the winter , the Ottoman fleet , with its 110 galleys and 30 , 000 troops , was able to use Toulon as a base to attack the Spanish and Italian coasts under Admiral Salih Reis . They raided Barcelona in Spain , and Sanremo , Borghetto Santo Spirito , Ceriale in Italy , and defeated Italo - Spanish naval attacks . Sailing with his whole fleet to Genoa , Barbarossa negotiated with Andrea Doria the release of Turgut Reis . France provided about 10 , 000 , 000 kilograms of bread to supply the Ottoman army during the 6 months it stayed in Toulon , and for the provisioning of the following summer ' s campaign and return to Constantinople . It seems the involvement of Francis I to this joint effort with the Ottomans were rather half - hearted however , as many European powers were complaining about such an alliance against another Christian power . Relations remained tensed and suspicious between the two allies . Consequences . A French - Habsburg peace treaty was finally signed at Crépy on 18 September 1544 , and a truce was signed between the Habsburg and the Ottomans on 10 November 1545 . The Habsburg emperor Charles V agreed to recognize the new Ottoman conquests . A formal peace treaty was signed on 13 June 1547 , after the death of Francis I . A local consequence of the siege was the reinforcement of the coast with defensive fortifications , especially the castles of Nice and Mont Alban , and the fort of Saint - Elme de Villefranche .