Aon Center (Chicago) the world headquarters of Aon and Amoco. Aon's US operations are still headquartered here. The building is also the co-headquarters of Kraft Heinz. The Standard Oil Building was constructed as the new headquarters of the Standard Oil Company of Indiana, which had previously been housed at South Michigan Avenue and East 9th Street. When it was completed in 1973, it was the tallest building in Chicago and the fourth-tallest in the world, earning it the nickname "Big Stan". (A year later, the Sears Tower took the title as Chicago's and world's tallest.) The building employs a tubular steel-framed structural system
Metropolitan Tower (Chicago) of this ornament, the building is sometimes referred to as the "Beehive Building." Just beneath the beehive are four carillon bells ranging in weight from 1,500 to 7,000 pounds, unused for many years until restored in 1979 for the Chicago visit of Pope John Paul II. At one time, the bells chimed the well-known Cambridge Quarters on the quarter-hours. The base has been altered from its original design: rectangular window openings replaced giant arches on Michigan Avenue and Jackson Boulevard. At one time, the thirtieth floor was the Straus Tower Observatory, which was open to the public for viewing the