The Capitol's great cast-iron dome is an astonishing feat of architecture and engineering. It was the Capitol's second dome, the earlier wooden one was removed as a precaution against fire. The replacement dome was planned by Thomas U. Walter, the architect of the Capitol extension, whose design was influenced by classical European domes. Iron brackets embedded in five million pounds of brickwork laid on the old stone walls hold an outer ring of 36 columns (one every 10 degrees). Thirty-six curving iron trusses rise to the lantern and support both the inner dome and the outer skin. Work began in 1855 with the removal of the old wooden dome.
In 1860, the New York foundry of Janes, Fowler, Kirtland & Company won the contract to finish the dome. At the outbreak of the Civil War the contractor was advised not to expect further payment but they decided to continue anyway. That decision inspired President Lincoln and others to see the dome as a sign that the nation would also continue. The last section of the Statue of Freedom was positioned on December 2, 1863, and the interior was finished in 1866. The dome's total cost was $1,047,291.