The central east-west corridor is referred to as the Great Experiment Hall because it chronicles in 16 murals the legislative milestones of three centuries, from the signing of the Mayflower Compact in 1629 to the enactment of women's suffrage in 1920. Thirty-two vignettes complementing the historical scenes are painted at the sides of the murals. In the ceiling 16 medallion portraits are painted in chronological order, and quotations appear above the 16 doorways. The corridor was dedicated in 1982, not long before artist Allyn Cox's death. Cliff Young, Cox's assistant, then began to refine details of Cox's sketches for the third corridor, but he died in 1986 before beginning to paint.
Cox first executed the murals in the eastern north-south corridor, starting work in 1973 and finishing in 1974. This corridor has been termed the Hall of Capitols because it features paintings of 16 different buildings that housed the Continental and United States Congresses from 1754 to 1865. Portraits of the nine men who served as Architect of the Capitol between 1793 and 1974 decorate the groined vaults of the ceilings. Painted in the barrel vaults of the ceilings are eight historic events that occurred during the first 65 years of the Capitol's existence. In lunettes on the walls, trompe l'oeil techniques use shades of gray to simulate sculpture. Two depict sculptures that had been displayed at the Capitol in the past: Horatio Greenough's George Washington and Giovanni Charles Micali's Tripoli Monument. Two depict Capitol sculptures that are more difficult to see because of their locations: the woodsman figure from Thomas Crawford's Progress of Civilization pediment above the Senate doors on the East Front and two figures from Carlo Franzoni's Justice in the Old Supreme Court Chamber.
In 1993-1994 the third series of murals, based on Cox's approved designs, was executed in the western north-south corridor by EverGreene Painting Studios, Inc. Called the Westward Expansion corridor, it includes maps and scenes showing the growth of the United States from early exploration through the acquisition of Alaska and Hawaii. As in the corridors that Cox executed, the scenes on the vaults are set above illusionistic architectural motifs and relief sculpture. Each map in the vaults is shown in the cartographic style appropriate to its historical period. Jeffrey Greene, the head of EverGreene Painting Studios, verified the geographical and historical accuracy of Cox's preliminary sketches, developed new scenes compatible with Cox's concept, and then submitted detailed sketches and small-scale oil paintings of each vault to the Architect of the Capitol for the necessary approval.
