(Guido Aretinus). Born in the 990’s; died May 17, 1050 (?). Italian musician.

Guido D’Arezzo was educated in a monastery near Ferrara. He was a Benedictine monk and a teacher of choral singing. For a while he worked in the monastery in Arezzo (Tuscany). Guido D’Arezzo is one of the outstanding reformers of medieval music. He introduced the use of the four-line staff system of notation in which the pitch of the sound is indicated by letters on every line. His reform of musical notation provided the means for accurate recording of musical works, played an important role in the development of the art of composing, and is the basis of the modern system of notation. Guido D’Arezzo invented solmization, the system of using syllables to denote the tones of a musical scale, which he used to make the teaching of singing easier. He introduced the six-tone musical scale (hexachord) with a specified scheme of intervals and a syllabic designation of the successive tones (ut, re, mi, fa, sol, la). These designations were derived from the first syllables of the first six lines of the Latin hymn to St. John (the legendary patron saint of singers).