[citation needed] The first known Bishop of Orvieto was John (about 590), and in 591 appears a Bishop Candidus; among its other prelates were Bishop Constantinus, O.P., sent by Pope Alexander IV in 1255 to Greece as his Legate, where he died in 1257;[3] In 1528 Pope Clement VII sought refuge at Orvieto, after the sack of Rome, and while there ordered the construction of the "Pozzo di San Patrizio" (the well of St. Patrick),[4] by Antonio da Sangallo; it was completed in the reign of Pope Paul III (1534–1549).

[5] Bishop Sebastiano Vanzi (1562–1570) participated in the 17th through 25th sessions of the Council of Trent (1562–1563) as one of the Definitori (legal draftsmen).

[6] In accordance with the decrees of the Council, he established the seminary of Orvieto as an institution; it was enlarged with a building of its own in 1645 by Cardinal Fausto Poli; later Giacomo Silvestri gave it the college and other property which was confiscated from the Jesuits (1773) when their religious order was suppressed.

[9] In 1695, the Chapter, which was the cathedral's administrative body, was composed of two dignities, the Archdeacon and the Provost, and sixteen Canons.

[19] A project begun on orders from Pope John XXIII, and continued under his successors, was intended to reduce the number of dioceses in Italy and to rationalize their borders in terms of modern population changes and shortages of clergy.

The former cathedral in Todi was to have the honorary title of co-cathedral, and its Chapter was to be called the Capitulum Concathedralis.

There was to be only one episcopal curia, one seminary, one ecclesiastical tribunal; and all the clergy were to be incardinated in the diocese of Orvieto-Todi.