medium-sized towns of the era are known to have proliferations of towers, such as the 72 up to 51 m height in San Gimignano. The medieval Egyptian city of Fustat housed many high-rise residential buildings, which Al-Muqaddasi in the 10th century described as resembling minarets. Nasir Khusraw in the early 11th century described some of them rising up to 14 storeys, with roof gardens on the top floor complete with ox-drawn water wheels for irrigating them. Cairo in the 16th century had high-rise apartment buildings where the two lower floors were for commercial and storage purposes and the multiple storeys above them were rented out to tenants. An early example of a city consisting entirely of high-rise housing is the 16th-century city of Shibam in Yemen. Shibam was made up of over 500 tower houses, each one rising 5 to 11 storeys high, with each floor being an apartment occupied by a single family. The city was built in this way in order to protect it from Bedouin attacks. Shibam still has the tallest mudbrick buildings in the world, with many of them over high. An early modern example of high-rise housing was in 17th-century Edinburgh, Scotland, where a defensive city wall defined the boundaries of the city. Due to the restricted land area available for development, the houses increased in height instead. Buildings of 11 storeys were common, and there are records of buildings as high as 14 storeys. Many of the stone-built structures can still be seen today in the old town of Edinburgh. The oldest iron framed building in the world, although only partially iron framed, is The Flaxmill (also locally known as the "Maltings"), in Shrewsbury, England. Built in 1797, it is seen as the "grandfather of skyscrapers", since its fireproof combination of cast iron columns and cast iron beams developed into the modern steel frame that made modern skyscrapers possible. In 2013 funding was confirmed to convert the derelict building into offices. Early skyscrapers In 1857, Elisha Otis introduced the safety elevator at the E.V. Haughwout Building in New York City, allowing convenient and safe transport to buildings' upper floors. Otis later introduced the first commercial passenger elevators to the Equitable Life Building in 1870, considered by some architectural historians to be the first skyscraper. Another crucial development was the use of a steel frame instead of stone or brick, otherwise the walls on the