The Expedition of Mostaganem occurred in 1558, when Spanish forces attempted to capture the city of Mostaganem. The expedition was supposed to be a decisive step in the conquest of the Ottoman base of Algiers, but it ended in failure, and has been called a "disaster".
Background
The harbour of Mostaganem had been captured by the Spanish from the Muslims in 1506. The harbour became part of numerous Spanish possessions on the coast of the Maghreb, which had been captured since 1496: Melilla (1496), Mers-el-Kebir (1505), Oran (1509), Bougie (1510), Tripoli (1510), Algiers, Shershell, Dellys, Ténès.
In 1516, Mostaganem was seized by Hayreddin Barbarossa from his base of Algiers. He then strengthened its defences, and the city became a rival of Oran. From 1519, Barbarossa placed himself under the protection of the Ottomans, thereby transforming Mostaganem into an Ottoman dominion.
Previous Spanish expeditions had taken place in 1543 and 1547, which failed as the Spanish forces were repulsed and then pursued in retreat by Turkish and tribal forces.
The expedition of 1558 to retake Mostaganem from the Ottomans followed a string of Ottoman successes in the Mediterranean, especially with the Siege of Tripoli in 1551, and the evacuation of Al-Mahdiyeh by the Spaniards. Concurrently, the corsairs of Barbary were operating from their base in Algiers.
Preparations
The Count of Alcaudete made preparations in Spain to recruit sufficient troops for his expedition. He recruited many soldiers from the Spanish nobility. He was at the head of an army of 10 to 11,000 men partly inexperienced (he had received authorization to recruit 8,000) to which are added the 1,200 experienced soldiers from the place of Oran and artillery, some field and siege guns. 6,000 men gathered in Cartagena under the orders of the Count and 5,000 men under the orders of one of his sons, Don Martin, embarked from Malaga.
At the same time Hassan Pasha returned from an indecisive campaign in Fez in March-April 1558 when he learned of the preparations for a Spanish raid from Oran.
To counter the Spaniards, Hassan Pasha's army then consisted of 15,000 men: 5,000 Turks and renegades, 1,000 spahis to which were added 6,000 cavalry, and 10,000 Arab infantry and according to B. de Moralès 8,000 seasoned soldiers, many Moorish infantry and 10,000 cavalry.
The Battle
On August 24 at 10 a.m., the Spaniards arrived under the walls of Mostaganem. Moorish and Turkish guards came out to push them back but they were beaten by the vanguard. They fled, leaving the city gates open. A sergeant then launched the assault which was stopped dead on the orders of Martín Alonso Fernández who stubbornly undertook a regular siege. This strategy appeared to be risky, the city could have been taken but against all odds Alcaudete had this sergeant arrested and punished for his bravery. When all the troops were gathered, a camp was set up on the heights out of reach of the defenders and the defense was prepared by digging a ditch and installing a field battery while the armies of Tlemcen and Algiers converged on a forced march towards the Spanish position. On August 25 at noon, the arrival of the beylerbey of Algiers near Mostaganem was announced. Alcaudete sent his son to make sure of the situation. In the evening, the Spanish troops weighed a surprise attack from the beylerbey camp allowing the troops to refuel but nothing was decided. The count wanted to wait firmly for the troops of the regency and confront them on the spot. However, while Alcaudete was still waiting for the necessary ammunition and supplies by sea which were carried by a ship and four brigantines with 600 men on board were armed but the ship having turned around, the four brigantines were attacked and taken by five Turkish galleys. Without food and without ammunition, Alcaudete understood that he could neither stand up to the troops of the regency of Algiers, nor sustain the siege against Mostaganem. Alcaudete made the decision to retreat during the night. The situation was perilous, facing the troops of Hassan Pasha and surrounded by a population of hostile Moors, he withdrew his exhausted troops.