The 16-story Monadnock Building located in Chicago and constructed in 1891 used 1.8 m (6 ft) thick unreinforced masonry walls to reach a height of 60 m (197 ft). The structure exists today as the tallest load-bearing unreinforced masonry building. The 15-story, 61.6 m (202 ft) tall Reliance Building built in 1895 used structural steel and introduced the first curtain wall system. Buildings now could be conceived as clad structural skeletons with building skins erected after the frame was constructed. The Reliance Building has changed use (office building converted to hotel), but still exists on State Street in Chicago. Steam and hydraulic elevators were tested for use in 1850. By 1873, Elisha Graves Otis had developed and installed steam elevators into 2000 buildings across America. In 1889, the era of the skyscraper was embraced with the first installation of a direct-connected, geared electric elevator.