The Aon Center, originally known as the Standard Oil Building, is a prominent skyscraper in Chicago completed in 1973. Designed by Edward Durell Stone and Perkins and Will, the building was initially clad in Italian Carrara marble. It soon proved problematic due to its thinness and susceptibility to cracking under Chicago's weather conditions. In 1974, a marble slab fell, prompting a significant safety concern. By the early 1990s, the entire façade was replaced with Mount Airy white granite to ensure structural integrity. Renamed the Aon Center in 1999, it stands as the third tallest building in Chicago, with a sleek modernist design that continues to be a significant part of the city's architectural heritage.