12th-century theologian, bishop of Savona, then archbishop of Milan from 1101 to 1116; b. Greece or Sicily, c. 1050; d. Rome, Aug. 6, 1117. Nothing is known of Peter's career or of his election to the See of Savona, but upon the death of Anselm IV de Buis (Sept. 11, 1101) Peter became the archbishop of Milan. His election displeased the reform party in Milan, and they appealed to King Liutprand, through whose intervention Peter was forced to leave Milan (1103) and appeal to Pope PaschalII. In a Roman council held in 1105, Peter's position was upheld, and he was restored to his see. However, he was again deposed by the civil authorities and given Jordanus as a successor in 1112. He then embarked on a voyage to the Near East and, after a sojourn in Jerusalem, visited the court of alexius comnenus in Constantinople. Invited to attend a synod held in the Emperor's presence, he pronounced a discourse justifying the use of the filioque in the creed; this greatly upset his Greek hosts, and John Phurnes felt himself obliged to reply.
Grossolano's position was based on the thesis that to deny that the Holy Spirit proceeds from the Son is to lower the Son's glory and His equality with the Father. Grossolano's intervention was ill taken and caused a further renewal of polemic between Byzantium and Rome on the question of the procession of the Holy Spirit and the use of unleavened bread in the liturgy. A second discourse to the Greeks, attributed to Grossolano, repeated the same argument with considerable documentation and closed with an invitation to the emperor to bring about the reunion of the churches. Eustratis of Nicaea says Grossolano spoke frequently at the synod, but there is no further record of these interventions.
In 1116 both Peter and the intruded archbishop of Milan, Jordanus, appealed to the Council of the lateran for a settlement of their rival claims; and despite the support of the pope, the Council decided that Peter should return to his first see at Savona. Peter preferred to retire to the Monastery of St. Sabas in Rome, where he died a year later.
Bibliography: Patrologia Latina 162:1005–15. Patrologia Graeca 127:909–919. landulphus junior, Historia Mediolanensis, Patrologa Latina 173:1447–1546. v. grumel, Dictionnaire de théologie catholique 12.2:1939; Échos d'Orient 22 (1933) 22–33. Bibliotheca casinensis, 5 v. (Monte Cassino 1873–94) 4:351–358, text. j. drÄseke, Byzantinische Zeitschrift 5 (1896) 328–329, Eustratis.