The most important writer upon music in the eleventh century, and one of the most famous in the history of the art, was a monk named Guido, living at Arezzo, in Tuscany, a Benedictine in the abbey of Pontose. He was a remarkably skillful teacher of ecclesiastical singing, both in his own monastery and at Rome, and in the effort to systematize the elements of music he introduced a number of important reforms, and is credited by later writers with many others which he did not himself originate, but which grew out of some of his suggestions. He is generally credited with having invented the art of solmization, the introduction of the staff, the use of the hand for teaching intervals, and the introduction of notes. He was not the first who introduced the staff. Hucbald, as we have already seen, employed the spaces between the lines for designating pitch. Between his time and that of Guido, one or more lines were introduced in connection with the neumae, as will be more particularly illustrated in chapter XV. Guido, however, employed both the lines and the spaces, but instead of notes he wrote the Roman letters upon the lines and spaces according to their pitch. The notes were invented shortly after his time. For determining the correct pitch of the notes of the scale he explains the manner of demonstrating them upon the monochord. He mentions organum and diaphony, and remarks that he finds the succession of fifths and fourths very tiresome. The last treatise of the thirteenth century was written by John Cotton, an English monk, whose entire theory of music is made up from the Greek works. [Illustration: Fig. 29. GUIDO OF AREZZO.] This summary of the didactic writers between Boethius and Franco at Cologne fully confirms the justice of the remark, in the chapter previous, concerning the influence of the Church upon music. At the very time when a well marked beginning was being made in counterpoint by the old French school at Paris, and when the English, Welsh and Scandinavian musicians were in possession of an art of expressive melody resting upon a simple harmonic foundation, these writers can find nothing to say but to repeat over and over again their tedious calculations concerning the intonations of _nete hypate_ and the other Aristoxinean notes in the enharmonic and chromatic genera, which had been dead names in the art of music for more than ten centuries.