Surfing was of profound religious importance to the ancient Hawaiians. The study of waves was called "ka nalu" and the memory of notable surfing feats was preserved in chants and songs ("meles") passed down since the 15th century. Many chiefs had a personal surf chant that celebrated their surfing prowess; this could be performed only by a professional chanter, one of which every chief maintained in his retinue. Despite claims by some historians that surfing was reserved strictly for the "alii" or Hawaiian hereditary rulers, Hawaiians of all classes and sexes, young or old, practiced the art.