Historically, pearls have been used as an adornment for centuries. They were one of the favourite gem materials of the Roman Empire; later in Tudor England, the 1500s were known as the pearl age. Pearls are unique as they are the only gems from living sea creatures and require no faceting or polishing to reveal their natural beauty. In the early 1900s, the first successful commercial culturing of round saltwater pearls began. Since the 1920s, cultured pearls have almost completely replaced natural pearls in the market.