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The Forgotten History Of Chicago Supertalls: Everything You Need To Know About Aon Center

It's Chicago's fourth-tallest building but often doesn't get the love of Willis Tower or John Hancock Center. But Aon Center has proven worthy of being included among Chicago's most influential supertalls.

Aon Center, Chicago, IL
One and Two Prudential Plaza, and Aon Center, Chicago

Today, our ongoing series on the forgotten history of Chicago supertalls takes a look at the history of the 43-year-old building, from its construction to its future. Here are five fun facts about Aon Center.

1. Its Nickname Is "Big Stan"

Aon Center, Chicago, in the early stages of construction, 1970

The Standard Oil Company of Indiana wanted to move its HQ from the South Loop to the East Side and commissioned Perkins+Will to design the building. Architect Edward Durell Stone's blueprints wound up being simple. Stone designed a tubular steel frame with V-shaped perimeter columns intended to resist earthquakes (we get them here), reduce sway, and maximize column-free space while minimizing column bending. Stone's designs proved so influential they would later be used in the construction of New York's World Trade Center. When Aon Center was topped out in 1973, it was Chicago's tallest building, and the fourth-tallest in the world, until Willis Tower took over both one year later. The building was originally called the Standard Oil Building and earned the nickname "Big Stan."

2. It Was The Tallest Marble Skyscraper In The World

Aon Center, Chicago, under construction in 1973

During construction, Aon Center was sheathed with 43,000 columns of Italian Carrara marble, which made the building the world's tallest marble-clad skyscraper. There was a bit of trial and error during the build-out. The marble was thinner than what was previously attempted in cladding a building; a 350-pound slab broke off the building on Christmas Day 1973, piercing the roof of the Prudential Center.

An inspection of the marble in 1985 later revealed significant cracks and bowing in the cladding. The marble was replaced with white granite between 1990 and 1992, resulting in its current look. Two-thirds of the discarded marble can be found in the landscaping of BP's Whiting, IN, refinery. The remainder was split and given to Governors State University and a company called Regalo, whose employees repurposed the marble into corporate gifts such as desk clocks and pen holders.

3. It's Changed Hands As Often As It's Changed Names

Aon Center, Chicago, IL

The building was rechristened the Amoco Building when Standard Oil changed its name in 1985. Amoco sold the building to The Blackstone Group in 1998, in what was believed to be a $440M deal. A year later, Aon Corp bought the naming rights as the primary tenant—it was the company's global HQ and still houses Aon's US operations. Piedmont Office Realty Trust (then known as Wells REIT) bought Aon Center for $475M in 2003 and held it before The 601W Cos acquired it for a record $712M last year.

4. An Observatory May Be In Its Future

Aon Center, Chicago, IL

When The 601W Cos bought Aon Center last year, the firm said it was considering building an observatory atop the 83-story building. 601W managing principal Mark Karasick believes the unobstructed views of Millennium Park and the south lakefront would be nice complements to the observation decks at Willis Tower and the John Hancock Center. If 601W moves forward with an observatory, Chicago would become the only city in North America with observatories atop three supertalls.

5. It's Well-Connected To The Loop

Aon Center, Chicago, IL

Despite its proximity to downtown, Aon Center can feel like it's miles away from the Loop on sweltering summer days and especially when we're buried beneath the snow, single-digit temps and biting lakefront winds of winter. Thankfully, the Pedway provides shelter from the elements, allowing tenants and visitors to get to and from other East Side buildings and Loop structures, and catch the Metra Electric and South Shore Lines. Bonus, you can grab a bite to eat and shop underground.