Under the reign of the Mamluk sultan al-Nasir Muhammad (1293-1341, including interregnums), Cairo reached its apogee in terms of population and wealth. A commonly-cited estimate of the population towards the end of his reign, although difficult to evaluate, gives a figure of about 500,000, making Cairo the largest city in the world outside China at the time. Despite being a largely military caste, the Mamluks were prolific builders and sponsors of religious and civic buildings. An extensive number of Cairo's historical monuments date from their era, including many of the most impressive. The city also prospered from the control of trade routes between the Indian Ocean and the Mediterranean. After the reign of al-Nasir, however, Egypt and Cairo were struck by repeated epidemics of the plague, starting with the Black Death in the mid-14th century. Cairo's population declined and took centuries to recover, but it remained the major metropolis of the Middle East.