The innovation came in the early eleventh century, when Guido of Arezzo (c. 991–1050), an Italian monk, devised a precise system for defining pitch. Guido was a leading music teacher and theorist in his day. As such, he was invited in about 1028 to Rome, where he presented a collection of religious anthems to Pope John XIX. Guido used a system of four horizontal lines (a staff) on which to chart pitch, and he used the syllables ut (later replaced with do), re, mi, fa, sol, and la to name the first six tones of the major scale. Before Guido developed his precise method for teaching music, singers had to learn melodies by memorizing them, a process that took many years. Using his notating system, singers were able to sight-read melodies. Guido’s famous treatise, Micrologus, was one of the most widely used instruction books of the Middle Ages (500–1350).