Classicism, based on the art and architecture of ancient Greece and Rome, may be best described as the style that never goes out of style. The first revival of Classicism began in 16th century Italy, spurred by a wave of awe-inspiring archeological discoveries from the ancient world, such as the Emperor Nero's legendary palace, the Domus Aurea in Rome.
Having captured the imagination of such geniuses as Michaelangelo, DaVinci, and Raphael, the style constantly evolved thru the next four centuries, spawning (amongst others) the Louis XVI and Empire styles of France, and England's Georgian, Adam, and Regency styles.
In America, Classicism was the founding architectural and decorative style of the 17th and 18th centuries. By the first half of the 19th century, the Federal style had morphed into the American Empire and the Greek Revival styles. After the Civil War the Renaissance Revival (or Italianate) and Beaux Art styles became hallmarks of the Gilded Age.