After the Great Chicago Fire leveled the city in 1871, the residents had a unique opportunity to completely rebuild from the ground up. The next two decades witnessed an explosion of architectural advancements in construction height and design, which resulted in the birth of the modern-day skyscraper. The architectural style of these early skyscrapers is known as the 19th Century Commercial. This style features a steel frame, a modest cornice, and large bands of windows. The tour begins with one of the world's first steel-frame buildings, the Reliance Building. The tour continues down through the Loop with stops at the Marquette Building, the Railway Exchange (now known as the Motorola Building), and the Monadnock Building. The tour concludes with the architecturally innovative Manhattan Building.