However, before considering the new diaphony, we have still to trace the further progress of the organum of Hucbald and Odo. The next theorist of importance was Guido of Arezzo. To Guido have been attributed at various times most of the important inventions and reforms of early polyphonic music, among them descant, organum and diaphony, the hexachordal system, the staff for notation, and even the spinet; but the wealth of tradition which clothed him so gloriously has, as in the case of many others, been gradually stripped from him, till we find him disclosed as a brilliantly learned monk and a famous teacher, author of but few of the works which possibly his teaching inspired. He has recently been identified with a French monk of the Benedictine monastery of St. Maur des Fosses.[66] He was born at or near Arezzo about 990, and in due time became a Benedictine monk. He must have had remarkable talent for music, for about 1022 Pope Benedict VIII, hearing that he had invented a new method for teaching singing, invited him to Rome to question him about it. He visited Rome again a few years later on the express invitation of Pope John XIX, and this time brought with him a copy of the _Antiphonarium_, written according to his own method of notation. The story goes that the pope was so impressed by the new method that he refused to allow Guido to leave the audience chamber until he had himself learned to sing from it. After this he tried to persuade Guido to remain in Rome, but Guido, on the plea of ill-health, left Rome, promising to return the following year. However, he accepted an invitation from the abbot of a monastery near Ferrara to go there and teach singing to the monks and choir-boys; and he stayed there several years, during which he wrote one of the most important of his works, the _Micrologus_, dedicated to the bishop of Arezzo. Later he became abbot of the Monastery of Santa Croce near Arezzo, and he died there about the year 1050. During the time of his second visit to Rome he wrote the famous letter to Michael, a monk at Pomposa, which has led historians to believe that he was actually the inventor of a new division of the scales into groups of six notes, called _hexachorda_, and a new system of teaching based on this division.