Consider a few traits: Thirty-nine of them have domes; a considerable majority feature symmetrical wings for senate and house chambers; porticos and rotundas seem almost obligatory; almost all are built of granite or limestone. 

Obviously, these traits bring to mind that most familiar of capitol buildings, the national one, and yet the imitative lineage is more complicated than that. The U.S. capitol derived inspiration from earlier state predecessors.

States selected the finest architects of their day to design their capitols about as often as they selected their finest citizens to be governors—not very frequently. The vast majority of these buildings were the work of architects of lesser-to-vanishing renown. There are a few works by eminent American architects, one by McKim Mead and White, two by Cass Gilbert, and one partially to Henry Hobson Richardson’s credit. And yet the first three of those are obvious experiments on familiar models, all looking far more like the national and state peers than anything else.

The capitol is a unique American building type. Like much of the built environment in the U.S., capitols are a bit more similar than you’d hope, and yet harbor plenty of intriguing variety. In 1976, Henry Russell Hitchcock wrote the only substantial appreciation of their form and design, Temples of Democracy: State Capitols of the U.S.A. He noted:

Skyscrapers and state capitols are America’s unique contribution to monumental architecture. The skyscraper is a product of function and structure; the state capitol owes its special character to symbolism. To most Americans today architectural symbolism means church design—the steeple and the pointed Gothic arch. Yet far more significant to the United States are earlier, Classically inspired architectural features, first built by colonial legislatures long before the opening guns of the Revolution. Their creators were legislators who saw in the dramatic possibilities of architecture a means of expressing the spirit of liberty. The vision was an accurate one: Those architectural features developed into symbols for the young nation, eventually taking on an abstract authority in the architecture of state capitols. Since the second decade of the nineteenth century the symbols have dominated every legislative building erected in the United States. Their story through two centuries of American building is a chronicle more continuous than any other, even that of the church and private house.

The Virginia capitol was the first to eschew the traditional colonial “state house” naming convention (which a number are still called) and invoke the grander antecedent of the Capitolium overlooking the Roman forum. The oldest State House, Maryland’s, preceded the Declaration of Independence, begun in 1772. It introduced spectators’ galleries and pioneered some aspects of the capitol form that have proven subsequently dominant, such as balanced legislative chambers and a central steeple or dome.

If the prevailing definition of “professional architect” was still nebulous in the early decades of the United States, almost none of the architects who designed capitols met it. Many were, in effect, designed by committees and executed by master builders. Some unlikely suspects had a hand in their creation. 

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