The fifth siege of Gibraltar, mounted between August 1349 and March 1350, was a second attempt by King Alfonso XI of Castile to retake the fortified town of Gibraltar. It had been held by the Moors since 1333. The siege followed years of intermittent conflict between the Christian kingdoms of Spain and the Moorish Emirate of Granada, which was supported by the Marinid sultanate of Morocco. A series of Moorish defeats and reverses had left Gibraltar as a Moorish-held enclave within Castilian territory. Its geographical isolation was compensated for by the strength of its fortifications, which had been greatly improved since 1333. Alfonso brought an army of around 20,000 men, along with his mistress and their five illegitimate children, to dig in to the north of Gibraltar for a lengthy siege. In the New Year of 1350, however, bubonic plague – the Black Death – broke out in the Castilian camp. Alfonso refused to abandon the siege but fell victim to the plague on 27 March 1350, becoming the only monarch to die of the disease.