I recently read an online column that referred to Washington, D.C., as "the nation's capitol." Oh, dear. I'm sure it was a slip of the keyboard, because we all know that Washington is the "capital," while the "Capitol" is the building in which Congress meets.
But a question occurred to me for the first time—why? Why does the building have an "o"? This turned out to be a more difficult question to answer than I had imagined. The Capitol's Web site's FAQ page does not answer it, and there is no SAQ page for Seldom Asked Questions. The history of the Capitol addresses why the building is placed where it is, but no source I found contemplated the question "Why is it called the Capitol?"
The only other "capitol" I could find was a fleeting reference to the Collis Capitolinus or Capitoline Hill in Rome, the site of the ancient Temple of Jupiter, now called Campidoglio.
I can only infer that our Capitol was named for the long-gone structure that was ancient Rome's preeminent temple. The Founding Fathers, many of whom were beneficiaries of a classical education, made reference to the Roman republic in their writings and organizations, such as the Society of the Cincinnati, based on the Roman consul, Cincinnatus, a farmer who led Rome in time of war and then returned to his farm. George Washington, even then thought of as America's Cincinnatus, was the society's first president.
Maybe I should let the folks who manage the Capitol Web site know about this.