Tomasso de Vio, a forty-eight-year-old Dominican and Scholasticist writing as Cajetan, becomes a cardinal in 1517 and is posted to Augsburg as papal legate.

A leading interpreter of the work of Thomas Aquinas, Cajetan’s commentary on Aquinas's Summa Theologiae is considered a classic of theology.

The Saxon Dominican provincial charges Luther with heresy, and he is summoned in 1519 to appear in Augsburg before the papal legate, Cardinal Cajetan.

Refusing to recant, Luther flees to Wittenberg, seeking the protection of the elector Frederick the Wise of Saxony.

When the Wittenberg faculty sends a letter to Frederick declaring its solidarity with Luther, the elector refuses to send Luther to Rome, where he will surely face imprisonment or death.

Luther, his cause supported by the German humanists, wins powerful popular support with three celebrated treatises of 1520, in which he states his views.

In “An Open Letter to the Christian Nobility of the German Nation Concerning the Reform of the Christian Estate,” he invites the German princes to take the reform of the church into their own hands.

In “A Prelude Concerning the Babylonian Captivity of the Church,” he attacks the papacy and the current theology of sacraments.

In “On the Freedom of a Christian Man,” he states his position on justification and good works.

The bull of Pope Leo X “Exsurge Domine,” issued on June 15, 1520, threatens Luther and Karlstadt with excommunication, and condemns several of their theses.

Luther has sixty days to recant.

Both Luther and Karlstadt have remained steadfast.

Johann Eck, as a papal legate in 1520, is largely responsible for the papal bull “Exsurge Domine” that results in Luther’s excommunication, under Decet Romanum Pontificem, on January 3, 1521.

Cardinal Thomas Cajetan, commonly Tommaso de Vio or Thomas de Vio, had helped in drawing up the bill of excommunication against Luther in 1519.

De Vio has been employed in several other negotiations and transactions, being as able in business as in letters.

In conjunction with Cardinal Giulio de' Medici in the conclave of 1521‑1522, he had secured the election of Adrian Boeyens, bishop of Tortosa, as Adrian VI.

He has retained influence under Clement VII, suffered a short term of imprisonment after the storming of Rome by the Constable of Bourbon and by Frundsberg (1527), had retired to his bishopric for a few years, and, returning to Rome in 1530, had assumed his old position of influence about the person of Clement, in whose behalf he has written the decision rejecting the appeal for divorce from Catharine of Aragon made by Henry VIII of England.

Nominated by Clement VII a member of the committee of cardinals appointed to report on the "Nuremberg Recess", he has recommended, in opposition to the majority, certain concessions to the Lutherans, notably the marriage of the clergy as in the Greek Church, and communion in both kinds according to the decision of the council of Basel.

Cardinal De Vio dies in Rome on Augusti 9,1534.