Taddeo Altini, O.S.A. (1609 – 27 August, 1685) was a Roman Catholic prelate who served as Bishop of Civita Castellana e Orte (1653–1685) and Titular Bishop of Porphyreon (1646–1653).^[1]

Taddeo Altini was born in 1603 in Camerino, Italy and ordained a priest in the Order of Saint Augustine.^[2][3] On 17 December 1646, he was appointed during the papacy of Pope Innocent X as Titular Bishop of Porphyreon.^[1][2] On 10 November 1653, he was consecrated bishop by Giovanni Battista Maria Pallotta, Cardinal-Priest of San Silvestro in Capite, with Celso Zani, Bishop Emeritus of Città della Pieve, and Alessandro Vittrici, Bishop of Alatri, serving as co-consecrators.^[2] On 10 November 1653, he was appointed during the papacy of Pope Innocent X as Bishop of Civita Castellana e Orte.^[1][2] He served as Bishop of Civita Castellana e Orte until his death on 27 August 1685.^[2]

While bishop, he was the principal co-consecrator of:^[2]

• Camillo Massimi, Titular Patriarch of Jerusalem (1654);
• Ambrogio Landucci, Titular Bishop of Porphyreon (1655);
• Sigismondo Isei, Bishop of Comacchio (1655); and
• Giovanni Battista Federici, Bishop of Sagone (1655).

• Cheney, David M. "Porphyreon (Titular See)". Catholic-Hierarchy.org. Retrieved January 4, 2019. (for Chronology of Bishops) ^{[self-published]}
• Chow, Gabriel. "Titular Episcopal See of Porphyreon (Israel)". GCatholic.org. Retrieved January 4, 2019. (for Chronology of Bishops) ^{[self-published]}
• Cheney, David M. "Diocese of Civita Castellana". Catholic-Hierarchy.org. (for Chronology of Bishops) ^{[self-published]}
• Chow, Gabriel. "Diocese of Civita Castellana (Italy)". GCatholic.org. (for Chronology of Bishops) ^{[self-published]}