or to New York's seven-floor Equitable Life Building, built in 1870. Steel skeleton construction has allowed for today's supertall skyscrapers now being built worldwide. The nomination of one structure versus another being the first skyscraper, and why, depends on what factors are stressed. The structural definition of the word skyscraper was refined later by architectural historians, based on engineering developments of the 1880s that had enabled construction of tall multi-storey buildings. This definition was based on the steel skeleton—as opposed to constructions of load-bearing masonry, which passed their practical limit in 1891 with Chicago's Monadnock Building. — Louis Sullivan's The Tall Office Building Artistically Considered (1896) Some structural engineers define a highrise as any vertical construction for which wind is a more significant load factor than earthquake or weight. Note that this criterion fits not only high-rises but some other tall structures, such as towers. Different organizations from the United States and Europe define skyscrapers as buildings at least 150 metres in height or taller, with "supertall" skyscrapers for buildings higher than and "megatall" skyscrapers for those taller than . The tallest structure in ancient times was the Great Pyramid of Giza in ancient Egypt, built in the 26th century BC. It was not surpassed in height for thousands of years, the Lincoln Cathedral having exceeded it in 1311–1549, before its central spire collapsed. The latter in turn was not surpassed until the Washington Monument in 1884. However, being uninhabited, none of these structures actually comply with the modern definition of a skyscraper. High-rise apartments flourished in classical antiquity. Ancient Roman insulae in imperial cities reached 10 and more storeys. Beginning with Augustus (r. 30 BC-14 AD), several emperors attempted to establish limits of 20–25 m for multi-storey buildings, but were met with only limited success. Lower floors were typically occupied by shops or wealthy families, with the upper rented to the lower classes. Surviving Oxyrhynchus Papyri indicate that seven-storey buildings existed in provincial towns such as in 3rd century AD Hermopolis in Roman Egypt. The skylines of many important medieval cities had large numbers of high-rise urban towers, built by the wealthy for defense and status. The residential Towers of 12th century Bologna numbered between 80 and 100 at a time, the tallest of which is the high Asinelli Tower. A Florentine law of 1251 decreed that all urban buildings be immediately reduced to less than 26 m. Even