Викепедия немного говорит http://ru.wikipedia.org/wiki/%D0%97%D0%B0%D0%BC%D0%BE%D0%BA_%D0%BF%D1%80%D0%B8%D0%BD%D1%86%D0%B5%D1%81%D1%81%D1%8B_%D0%9E%D0%BB%D1%8C%D0%B4%D0%B5%D0%BD%D0%B1%D1%83%D1%80%D0%B3%D1%81%D0%BA%D0%BE%D0%B9