Mather Tower (later Lincoln Tower, as designated on the Michigan–Wacker Historic District roster; now identified primarily by its address) is a Neo-Gothic, terra cotta-clad high-rise structure in Chicago, Illinois, United States. It is located at 75 East Wacker Drive in the downtown "loop" area, adjacent to the Chicago River. The -high building is sometimes called "The Inverted Spyglass" by Chicagoans due to its highly unusual design, an 18-story octagonal tower atop a more conventional 24-story rectangular "box." Briefly the tallest building in Chicago at the time of its completion in 1928, it remains the city's most slender high-rise structure at only at its base. The interior space within the upper octagonal spire contains the least square footage per floor of any Chicago skyscraper. History It was designed by Herbert Hugh Riddle (1875–1939), the architect of the Chicago Theological Seminary, as headquarters for the Mather Stock Car Company, a builder of rail cars for transporting livestock. Its design was greatly influenced by the pioneering Chicago Zoning Ordinance of 1923, which placed no limit on the height of new buildings as long as the surface area of the structure's uppermost floor did not exceed 25% of its footprint. This resulted in a multitude of tall, slender, "setback" towers, of which the Mather is an extreme and unusual example. The top floor of the octagonal spire has only of floor space. Mather Company's founder, Alonzo Mather (a descendant of Cotton Mather) is said to be responsible for a number of the building's distinctive design features, including the octagonal tower. Initial plans called for construction of a second, identical building on North Michigan Avenue, behind the Mather and connected to it by a ground-floor arcade, but onset of the Great Depression in 1929 forced its cancellation. By the 1990s the building had fallen into significant disrepair. In 2000 the 4-story "cupola" at the top of the building was demolished because of structural deterioration and safety concerns, after chunks of terra cotta began falling from the facade. Damage was sufficiently extensive that consideration was given to dismantling the remaining 17 stories of the octagonal spire as well. In 2000 Masterworks Development Corporation purchased the structure and undertook a complete restoration. In November 2002, the final phase of the project was initiated when a helicopter lifted the steel framework for a new cupola from a river barge to the top of the tower. The lower, rectangular