Historic Periods and Art Movements
The names of historic eras are generally lowercased, unless they derive from proper nouns.
However, some periods are traditionally capitalized, especially to avoid confusion with common usage: the Common Era, the Counter-Reformation, the Dark Ages, the Enlightenment, the Gay Nineties, the Gilded Age, the Jazz Age, the Middle Ages, the Progressive Era, the Reformation, the Renaissance, the Restoration, the Roaring Twenties.
Nouns and adjectives designating cultural movements, styles, and schools—artistic, architectural, musical, etc.—are capitalized if they derive from proper names: Aristotelian, Cartesian, Gregorian, Keynesian, Platonism, Pre-Raphaelites. In other cases they are not generally capitalized, though a few may be to distinguish them from words used in everyday speech (Cynicism, New Criticism) or when capitalized in the original foreign language (Arte Povera, Bauhaus, Dada). The lowercase style is preferred to avoid an undesirable profusion of capitals.