Who was the first to identify notes on a scale such as do re mi and fa?

The system of identifying musical notes using syllables was developed by Guido d'Arezzo, also known as Guido of Arezzo, in the 11th century. Guido was an Italian Benedictine monk and music theorist who lived from about 990 to 1050. He created the "Guidonian hand", a mnemonic system for learning the notes of the diatonic scale, where each note was associated with a syllable.