Petrus Helias is well known as a grammarian since his commentary, or rather summa, of Priscian's Institutiones Grammaticae enjoyed a lasting popularity in the Middle Ages. However, his rhetorical summa, too, should be taken into consideration, since it was widely read in the Middle Ages, and was as popular as the earlier, rhetorical commentaries by William (of Champeaux?) and Thierry of Chartres (from the turn of the century and the 1130s). We do not know much about Peter's life, but according to William of Tyre he came from Poitiers and was a pupil of Thierry of Chartres; in both cases, the information is substantiated by other sources. Doctrinally he was influenced by Thierry in both grammar and rhetoric, as well as by the twelfth-century humanist, philosopher, and grammarian, William of Conches. Peter's school was sought by such ambitious students as John of Salisbury, William of Tyre, and many others. He is mentioned by the author of the Metamorphosis Goliae (ca. 1140) among the famous Parisian masters.