In 1943, Chicago's Pizzeria Uno developed the first deep-dish pizza. Rather than a flat crust, a deep-dish pizza has a thick flour and cornmeal pizza crust that is pressed into a deep, steel, pie-like pan. In terms of the toppings, the order of the sauce and cheese is reversed. The cheese is found on the bottom layer, followed by meat and veggie toppings, and finally covered in a chunky tomato sauce.
Source: Flickr user maveric2003