Ever heard of the Dark Ages? (The Dark Ages: coming soon to a theater near you.)
Well, that's just a nasty name that some Italian guy gave to the Medieval Period or Middle Ages, a period that lasted roughly between 500 and 1500 CE. Don't quote those dates, though, or you're likely to get into some heated debates with tweed-sporting intellectuals.
This period fell smack dab between the classical period and the Renaissance, and compared to the two, it was, um, kind of a dark and stormy time. The Inquisition, feudalism, and some other not-so-fun things went down in this millennium. But that's not the only reason it was so dark. See, the Renaissance peeps were pretty high on themselves and all about recreating what went down in the classical period. So anything that came between them and their ancient inspiration was considered, you know, just the middle.
As for literature, the genre of romance was in fashion, with its emphasis on courtly love and knights and chivalry. The Song of Roland and Beowulf were already going by the 11th century, but most of what we know as Medieval literature was late-Medieval. Think The Canterbury Tales, The Divine Comedy, Sir Gawain and the Green Knight, and Le Morte d'Arthur.
The Romantics and the Victorians were majorly influenced by Medieval art. And really, any time you talk about a knight in shining armor, you should thank those Medieval authors. Without them, we'd all still be damsels in distress.