The dome of the US Capitol is so familiar that we take it for granted like our furniture. And yet, the US Capitol is a building without precedent. There is really nothing else like it, a palace and temple built to house a national legislature. The Capitol predates all of the parliamentary buildings of Europe, including London's Houses of Parliament. The English House of Commons met for centuries in St. Stephen's church which formerly stood in the confines of Westminster Palace. Its present chamber is a post World War II rebuild of a structure built in the mid 19th century. The Roman Senate met in its own house in the Forum (the present structure dates from the time of the Emperor Diocletian), and also in other places. It was meeting in the theater of Pompey when Julius Caesar was murdered. The Athenian Assembly met on a slope of the Pnyx hill through its entire history.
George Washington took an active interest in the design of the city that bears his name. The architect Pierre L'Enfant intended a great legislative house to be the centerpiece of his plan for the city. Washington wanted the building to be much more than a simple legislative chamber. He wanted a "temple" to liberty, a large monumental centerpiece that embodied the idea of popular sovereignty. It was Washington who coined the term "Capitol" that we use today, after the Roman Capitol, the temple to Jupiter on the Capitoline hill, the most important temple in Rome. Washington wanted the new American Capitol to face east toward the rising sun, an enduring testament to the "Novus Ordo Seclorum."
Washington chose the entry of Dr. William Thornton as the winner in the competition for the design of the new Capitol, praising it for its "elegance and simplicity." Thornton's design was for a smaller version of the Roman Pantheon with a shallow dome flanked by legislative chambers for the House and Senate each. Only the Senate wing was completed from Thornton's design. It was burned by the British army in 1814 during the War of 1812 (a calamity that remains unknown to most Americans; "What say ye we adjourn this Yankee parliament?" said a British soldier as he set a pile of desks and furniture on fire in the Senate chamber).
"Temple of Liberty," a political print from the 1780s commenting on the ratification of the new constitution.
Washington was not the only one who thought of the Capitol as a kind of temple. The idea of the Constitution as a kind of edifice, a temple with the states or the people as its supporting pillars, was common in political commentary of the time. The Capitol as built is a version of the Constitution in stone. The Roman classicism is very deliberate. The founders, including Washington, were all very well read in Classical literature, especially the Greek and Roman historians. The design of the Capitol deliberately recalls those ancient first experiments in democratic and republican rule in Greece and Rome.
Above is the oldest surviving photograph of the US Capitol. This is how it was completed by architects Benjamin Henry Latrobe and Charles Bullfinch. Bullfinch gave the Capitol the prominent wood and copper dome that appears in this photograph. The ambitions of Congress were not satisfied with the comparatively modest dome of Thornton's original design. This design would not last for long. Quickly, the country outgrew its Capitol, and a new larger building was required to house a much bigger legislature.
Architect Alexander Jackson Davis' drawing of the interior of Bullfinch's Capitol rotunda in the 1840s
The Philadelphia architect Thomas U. Walter was hired to design extensions for the Capitol; new larger chambers for the House and Senate. Bullfinch's wood and copper dome which once seemed too large now seemed too small. Walter was requested to design a new larger dome for the expanded Capitol.
Walter's design for a new much larger dome over the original rotunda is a combination of classical design and modern engineering. It is based on Wren's design for the dome of St. Paul's Cathedral in London, as reinterpreted by Soufflot in his dome for the Paris Pantheon (both of those domes were in turn modeled on the Tempietto designed by Bramante in Rome, which was modeled on round Roman temples like the "Temple of the Sibyl" at Tivoli, to complete the Classical pedigree). Unlike those earlier domes built of brick and marble, Walter's Capitol dome is built largely of cast iron. What we assume to be marble is in fact cast iron painted to look like marble. The dome is painted with a fresh coat carefully mixed to match the marble every 4 years.
When the Civil War broke out, most people expected, and demanded, that construction on the dome would stop. The labor and the material were more desperately needed for the war effort, especially with rebel troops encamped within sight just across the Potomac river. Lincoln decided to continue the construction, even with Confederate campfires visible from the White House. The dome would rise as testament to the durability of the Union and its founding principles.
Interior of the Capitol dome today with Constantino Brumidi's Apotheosis of Washington in the oculus.
Brumidi's Apotheosis of Washington showing a deified Washington with personifications of the original 13 states, and below, the gods Neptune, Mercury, Vulcan, Ceres, and Minerva standing for trade, commerce, industry, agriculture, and science respectively together with the goddess of Liberty slaying Tyranny.
The Capitol dome acquired its meaning through history. Thornton originally intended the dome to be a reminder of the Roman origins of republican government. As the building and its dome grew, it came to be associated with the imperial expansion of the United States. It was Lincoln and the experience of the Civil War that returned the Capitol to Washington's original intention to create a Temple to Liberty. Only now the concept of Liberty changed in the wake of the war from the privilege of freeborn white male property owners to a birthright of all Americans. The great Capitol dome, a traditional design in a modern material, becomes an embodiment of the timeless and expanding ideal of universal enfranchisement and popular sovereignty.