A number of ancient civilizations, including the Thracians, Ancient Greeks, Romans, Ostrogoths, Slavs, Varangians and especially Bulgars, have left their mark on the culture, history and heritage of Bulgaria. Because of this Bulgarian nation has one of the richest folk heritage in the world. Thracian artifacts include numerous tombs and golden treasures, while ancient Bulgars have left traces of their heritage in music and early architecture. Thracian rituals such as the Zarezan, Kukeri and Martenitza are to this day kept alive in the modern Bulgarian culture.