The United States Capitol dome is the massive dome

Dome

A dome is a structural element of architecture that resembles the hollow upper half of a sphere. Dome structures made of various materials have a long architectural lineage extending into prehistory....

 situated above the United States Capitol

United States Capitol

The United States Capitol is the meeting place of the United States Congress, the legislature of the federal government of the United States. Located in Washington, D.C., it sits atop Capitol Hill at the eastern end of the National Mall...

 which reaches upwards to 288 feet (87.8 m) in height and 96 feet (29.3 m) in diameter. The dome was designed by Thomas U. Walter

Thomas U. Walter

Thomas Ustick Walter of Philadelphia, Pennsylvania was an American architect, the dean of American architecture between the 1820 death of Benjamin Latrobe and the emergence of H.H. Richardson in the 1870s...

, the fourth Architect of the Capitol

Architect of the Capitol

The Architect of the Capitol is the federal agency responsible for the maintenance, operation, development, and preservation of the United States Capitol Complex, and also the head of that agency. The Architect of the Capitol is in the legislative branch and is responsible to the United States...

, and constructed between 1855 and 1866 at a cost of $1,047,291.

First dome

The cast iron

Cast iron

Cast iron is derived from pig iron, and while it usually refers to gray iron, it also identifies a large group of ferrous alloys which solidify with a eutectic. The color of a fractured surface can be used to identify an alloy. White cast iron is named after its white surface when fractured, due...

 dome of the United States Capitol is not the first dome to sit above the building, but the second. The origin of the first dome began with the Capitol design contest sponsored by Secretary of State

United States Secretary of State

The United States Secretary of State is the head of the United States Department of State, concerned with foreign affairs. The Secretary is a member of the Cabinet and the highest-ranking cabinet secretary both in line of succession and order of precedence...

 Thomas Jefferson

Thomas Jefferson

Thomas Jefferson was the principal author of the United States Declaration of Independence and the Statute of Virginia for Religious Freedom , the third President of the United States and founder of the University of Virginia...

, at the behest of President

President of the United States

The President of the United States of America is the head of state and head of government of the United States. The president leads the executive branch of the federal government and is the commander-in-chief of the United States Armed Forces....

 George Washington

George Washington

George Washington was the dominant military and political leader of the new United States of America from 1775 to 1799. He led the American victory over Great Britain in the American Revolutionary War as commander-in-chief of the Continental Army from 1775 to 1783, and presided over the writing of...

, in 1792. The winner of the contest, Doctor William Thornton

William Thornton

Dr. William Thornton was a British-American physician, inventor, painter and architect who designed the United States Capitol, an authentic polymath...

, called for a dome in his original design for the building. Most vividly, Thornton drew upon the Roman Pantheon

Pantheon, Rome

The Pantheon ,Rarely Pantheum. This appears in Pliny's Natural History in describing this edifice: Agrippae Pantheum decoravit Diogenes Atheniensis; in columnis templi eius Caryatides probantur inter pauca operum, sicut in fastigio posita signa, sed propter altitudinem loci minus celebrata.from ,...

 for inspiration with the Neoclassical

Neoclassical architecture

Neoclassical architecture was an architectural style produced by the neoclassical movement that began in the mid-18th century, manifested both in its details as a reaction against the Rococo style of naturalistic ornament, and in its architectural formulas as an outgrowth of some classicizing...

 dome and associated portico

Portico

A portico is a porch leading to the entrance of a building, or extended as a colonnade, with a roof structure over a walkway, supported by columns or enclosed by walls...

. However, Thornton never received the chance to build the dome he envisioned.

Nor, however, did Thornton's replacement as the second Architect of the Capitol, Benjamin Henry Latrobe, gain the opportunity to build the first dome for the Capitol. Rather, Latrobe was kept busy repairing, rebuilding, and completing the north and south wings of the building until his departure in 1817. Instead the job fell to Latrobe's successor, the third Architect of the Capitol, Charles Bulfinch

Charles Bulfinch

Charles Bulfinch was an early American architect, and has been regarded by many as the first native-born American to practice architecture as a profession....

. Bulfinch was responsible for the construction of the first dome in the nation, which he designed and built for the Massachusetts Statehouse in 1787.
Bulfinch began by adopting the suggestion of a drum, upon which the dome would sit, that was added to the Capitol designs by his predecessor, Latrobe. In contrast, however, the dome that eventually rose under Bulfinch's oversight was taller than any previous design and taller than his own preference. In an account written years later, Bulfinch stated that the dome was made loftier at the request of James Monroe

James Monroe

James Monroe was the fifth President of the United States . Monroe was the last president who was a Founding Father of the United States, and the last president from the Virginia dynasty and the Republican Generation...

's administration. In 1822, Bulfinch requested funds for the construction of the center of the building, and President Monroe signed off on an appropriation of $120,000. This included the building of a two-dome structure, a stone interior dome to rise 96 feet (29.3 m) above the rotunda

United States Capitol Rotunda

The United States Capitol rotunda is the central rotunda of the United States Capitol in Washington, D.C.. Located below the Capitol dome, it is the tallest part of the Capitol and has been described as its "symbolic and physical heart."...

 floor (matching the dimensions of the Pantheon), and a wooden exterior dome that would rise to 140 feet (42.7 m). Set at the crown of the exterior dome was a 24 feet (7.3 m) wide oculus

Oculus

An Oculus, circular window, or rain-hole is a feature of Classical architecture since the 16th century. They are often denoted by their French name, oeil de boeuf, or "bull's-eye". Such circular or oval windows express the presence of a mezzanine on a building's façade without competing for...

, which provided illumination to the rotunda floor below. Bulfinch completed the project in 1823.

For more than two decades, the green copper

Copper

Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...

 dome of the Capitol greeted visitors to the nation's capitol, until the 1850s. Due to the growth of the United States

Territorial acquisitions of the United States

This is a simplified list of United States territorial acquisitions, beginning with American independence. Note that this list primarily concerns land acquired from other nation-states; the numerous territorial acquisitions from American Indians are not listed here.-1783-1848:*The 1783 Treaty of...

 and the expansion and addition of new states, the size of the United States Congress

United States Congress

The United States Congress is the bicameral legislature of the federal government of the United States, consisting of the Senate and the House of Representatives. The Congress meets in the United States Capitol in Washington, D.C....

 had grown accordingly and pushed the limits of the capacity of the Capitol. Under the guidance of the fifth Architect of the Capitol, Thomas U. Walter, extensions were built onto the north and south wings of the building. In the process, the new, longer building made the original Bulfinch dome appear aesthetically displeasing (and had been the source of much prior criticism as well). Congress, after lobbying by Walter and Montgomery C. Meigs

Montgomery C. Meigs

Montgomery Cunningham Meigs was a career United States Army officer, civil engineer, construction engineer for a number of facilities in Washington, D.C., and Quartermaster General of the U.S. Army during and after the American Civil War....

 (then Supervising Engineer), passed legislation to build a bigger dome in 1855.

Second (current) dome

Plans began in May 1854 to build a new cast-iron dome for the United States Capitol, sold on the aesthetics

Aesthetics

Aesthetics is a branch of philosophy dealing with the nature of beauty, art, and taste, and with the creation and appreciation of beauty. It is more scientifically defined as the study of sensory or sensori-emotional values, sometimes called judgments of sentiment and taste...

 of a new dome, as well as the utility of a fire-proof one. Influenced by the great domes of Europe, Walter paid particular attention to the Pantheon

Panthéon, Paris

The Panthéon is a building in the Latin Quarter in Paris. It was originally built as a church dedicated to St. Genevieve and to house the reliquary châsse containing her relics but, after many changes, now functions as a secular mausoleum containing the remains of distinguished French citizens...

 of Paris

Paris

Paris is the capital and largest city in France, situated on the river Seine, in northern France, at the heart of the Île-de-France region...

, St Paul's Cathedral

St Paul's Cathedral

St Paul's Cathedral, London, is a Church of England cathedral and seat of the Bishop of London. Its dedication to Paul the Apostle dates back to the original church on this site, founded in AD 604. St Paul's sits at the top of Ludgate Hill, the highest point in the City of London, and is the mother...

 in London

London

London is the capital city of :England and the :United Kingdom, the largest metropolitan area in the United Kingdom, and the largest urban zone in the European Union by most measures. Located on the River Thames, London has been a major settlement for two millennia, its history going back to its...

, St. Peter's Basilica

St. Peter's Basilica

The Papal Basilica of Saint Peter , officially known in Italian as ' and commonly known as Saint Peter's Basilica, is a Late Renaissance church located within the Vatican City. Saint Peter's Basilica has the largest interior of any Christian church in the world...

 in Rome

Rome

Rome is the capital of Italy and the country's largest and most populated city and comune, with over 2.7 million residents in . The city is located in the central-western portion of the Italian Peninsula, on the Tiber River within the Lazio region of Italy.Rome's history spans two and a half...

 and Saint Isaac's Cathedral

Saint Isaac's Cathedral

Saint Isaac's Cathedral or Isaakievskiy Sobor in Saint Petersburg, Russia is the largest Russian Orthodox cathedral in the city...

 in Saint Petersburg

Saint Petersburg

Saint Petersburg is a city and a federal subject of Russia located on the Neva River at the head of the Gulf of Finland on the Baltic Sea...

. William Allen, Historian of the Capitol, described Walter's first design as,

"...a tall, ellipsodial dome standing on a two-story drum with a ring of forty columns forming a peristyle surrounding the lower half of the drum. The upper part of the drum was enriched with decorated pilasters upholding a bracketed attic. Crowning the composition was a statue standing on a slender, columned tholus..."

Walter drafted a seven-foot (two-meter) drawing of the aforementioned design and displayed it in his office, where it drew the excited attention of members of Congress in 1854. A year later, on March 3, 1855, President Franklin Pierce

Franklin Pierce

Franklin Pierce was the 14th President of the United States and is the only President from New Hampshire. Pierce was a Democrat and a "doughface" who served in the U.S. House of Representatives and the Senate. Pierce took part in the Mexican-American War and became a brigadier general in the Army...

 signed off on the appropriation of $100,000 to build the dome. Construction began after some practical changes to the original design (such as the reduction of the columns from forty to thirty-six) in September of that year with the removal of the dome raised by Charles Bulfinch. A unique scaffold was built inside the rotunda, designed to keep weight away from the weak center area of the floor, and a crane was set within to run on a steam-powered engine (fueled from the salvaged wood from the old dome).

Over the next eleven years, the dome designed with an interior dome and exterior dome rose over the nation's capitol. By December 2, 1863, Walter was able to set the Statue of Freedom

Statue of Freedom

The Statue of Freedom — also known as Armed Freedom or simply Freedom — is a bronze statue designed by Thomas Crawford that, since 1863, has crowned the dome of the U.S. Capitol in Washington, D.C.. Originally named Freedom Triumphant in War and Peace, official U.S...

atop the dome. This was not accomplished until after Walter had been forced to revise the design of the dome to handle the statue, which had been delivered taller and heavier than requested. Yet, the man who designed the dome did not see its total completion, due to Thomas Walter resigning in 1865. His replacement, Edward Clark

Edward Clark (architect)

Edward Clark was an American architect who served as Architect of the Capitol from 1865 to 1902.Edward Clark was Thomas U. Walter's student, chief assistant, and successor. Prior to working with Walter, he had received training in freehand and mechanical drawing as well as engineering...

, assumed the role of finishing the last aspects of the dome. Just over a month later, in January 1866, Constantino Brumidi

Constantino Brumidi

Constantino Brumidi was an Greek/Italian-American historical painter, best known and honored for his fresco work in the Capitol Building in Washington, DC.-Parentage and early life:...

 – who had been hired to paint a fresco

Fresco

Fresco is any of several related mural painting types, executed on plaster on walls or ceilings. The word fresco comes from the Greek word affresca which derives from the Latin word for "fresh". Frescoes first developed in the ancient world and continued to be popular through the Renaissance...

 on a platform above the interior dome's oculus – removed the scaffolding used during his work on the Apotheosis of Washington. This signaled the end of construction for the United States Capitol dome.

Some 8,909,200 pounds (4,041.2 metric tons) of iron were ultimately used in the construction that ran virtually eleven years. Inside, the interior dome rises to 180 feet (54.9 m) over the rotunda floor, and outside, the exterior dome ascends to 288 feet (87.8 m) including the height of the Statue of Freedom. The total cost of the dome was valued at $1,047,291.

Visitation of the dome is highly restricted, usually offered only to members of Congress and their select guests. Access is further restricted by the weather, since summer heat trapped under the dome may make the area unbearable. Visitors ascend a series of metal stairs between the inner and outer domes. They eventually wind their way to a balcony just underneath the Apotheosis of Washington. When looking up from the rotunda floor, you can barely make out the railing some 180 feet (54.9 m) above the rotunda floor. From this view, the painting is curved and distorted. From the balcony, metal stairs take visitors over the painting and up to the outside balcony under the tholos directly beneath the Statue of Freedom. Additional stairs lead up into the statue for maintenance.

Within the columned tholus upon which stands the statue of Freedom, there are two lights which serve as signifiers to the people of Washington and the nation that either one or both houses of Congress are in night sessions. The white light signifies that the House of Representatives is in night session. The red light signifies that the Senate is in night session. When both white and red lights burn together, they signify that the two houses of Congress are each in night sessions or that the two houses are in joint night session.