Selim sent to Kheir-ed-Din 2000 Janitschars, well realizing the importance of using Algiers to block the progress of Charles V in his North African ambitions. Four thousand men were also recruited in Anatolia to defend the Moslem cause. It was a critical time, when the Viceroy of Sicily (1519), at the head of an armada of forty ships, appeared off Algiers. The Spaniards were beaten off, and many of the ships were lost in a storm. An even greater success for Moslem arms was the conquest, ten years later, of the citadel of Peñon, which commanded the harbor of the city that had for long been in the hands of the Spaniards. The island on which it stood was, by instructions from Kheir-ed-Din, joined to the mainland, and so an impregnably fortified harbor was constructed, which turned Algiers into the lasting home of those Barbary pirates that were for so long the plague of the Mediterranean commerce. In 1535, Tunis was captured by Charles V in person, that monarch’s great expedition of 400 ships and 30,000 men having proved too strong for Kheir-ed-Din, who had hurried to save the place with only 9000 men. At Algiers, the Emperor’s next objective, Kheir-ed-Din could not take part personally in the work of defense, since he was not kept in command of the Turkish fleet. The government of Algiers was turned over to Hassan Aka, no idle leader. The Christian Emperor’s armada was calculated to inspire terror; when it gathered at Spezzia, in August, 1541, it numbered 65 galleys and 451 transports, ready to embark the 29,000 troops, German, Italian, and Spanish, and the members of the Knights of Malta. In addition to the Emperor, who was in command, there were a large number of high officers of the various arms, and members of the nobility from Charles V’s wide domains. To oppose this brilliant host, Hassan had only 800 Turks, 5000 Moors, some Moriscos from Spain, and a few renegades from the Island of Majorca. There were rumors of treachery on the part of Hassan, but when the actual attack was made, nothing was left undone by him to keep up an effective resistance. He was helped by a severe storm, which caused much damage to the fleet; many ships were driven ashore, where the crews were attacked and the cargoes seized. An attempt to attack one of the forts by which the city was defended failed; the imperial troops got near the walls, but no farther; even the heroism of the Knights of Malta failed to save the day. The Spanish admiral, Doria, insisted that the expedition should reimbark, as his ships could not hold their anchorage. No other attempt on such a scale was made to arrest the progress of the Turkish vassal powers in North Africa. Tripoli was conquered in 1556, and there was incessant warfare with the Sherif of Fez, and also with the Spaniards, who still continued to hold Oran.