He had been destined for the church, was tonsured at seven, and
        made a cardinal deacon at thirteen. After studying theology and Canon
        Law, he returned to Florence, was exiled with his brother as a result
        of the French campaign in 1494, visited France, the Low Countries, and
        the empire, and returned to Rome until sent as legate to Bologna in
        1511.
              He led a papal army against Florence when his native city
        declared itself for the Pisan cardinals, was captured at Ravenna in
        April 1512, escaped, and finally regained control of Florence in a
        bloodless coup on 14 September 1512. He became its effective ruler,
        vicariously through his younger brother even during his pontificate.
           As a result of Pope Julius II's determination to stamp out simony,
        the election of his successor---the thirty-seven-year-old Giovanni de'
        Medici, elected on 11 March 1513---was a straightforward contest
        between older and younger generations. The Pisan cardinals, who had
        been deposed by Julius II, had been excluded, and the conclave lasted
       eight days. The new pope was ordained priest on 15 March, consecrated 
        bishop two days later, and was enthroned as Pope, only two days after
        that.
               His policy largely concerned the protection of Florentine
        interest and the advancement of his family. His great-niece,
        Catherine, was married to the future Henri II, King of France. In 1513
        he reluctantly allied with the Emperor Maximilian, Spain and England,
        in an attempt to keep the French, allied with Venice, out of Lombardy.
              Leo closed the fith Lateran Council on 16 March 1517, ratified
        the concordat with France, confirmed the censorship of books
        introduced by Alexander VI, defined the individuality of the human
        soul, and imposed a tithe for war against the Turks. Also in 1517, Leo
        uncovered a conspiracy among disaffected cardinals to poison him. He
        had the leader executed, had several imprisoned and heavily fined, and
        created thirty-one new cardinals on 1 July 1517.
              After initially opposing Emperor Charles V, Leo concluded an
        anti-French alliance with him, leaving Wolsey's England to balance
        French power against the Habsburgs. Leo had spent huge amounts of
        papal funds on the Urbino war, the papal court, and the Pope's
        artistic patronage. He immensely increased the sale of offices, pawned
        furniture and plate, and renewed the indulgence decreed by Julius II
        for the new St.Peter's. There was strong German feeling against the
        collection for Rome of German money, and it was the preaching of this
        indulgence which moved Luther to contest the doctrinal justification
        for it, offering in 1517 to dispute his famous list of ninety-five
        theses.
              Leo tried to enlist the support from Frederick of Saxony, and a
        debate took place in the summer of 1519 between Johannes Eck, a
        professor of theology at Ingolstadt, and Luther, in which Luther
        contested both the divine institution of the papacy, considered
        offensive but not necessarily heretical, and the infallibility of
        general councils, which enabled Eck to claim victory.
              On 15 June 1520, Leo published the bull "Exsurge Domine",
        condemning Luther on forty-one counts, but not as a heretic. Luther's
        works became more radical that autumn, and on 10 December 1520 he
        tossed a copy of the bull into a bonfire of papal documents. Leo
        reacted by excommunicating him on 3 January 1521. On 11 October of
        that year he bestowed on Henry VIII the title of "Defender of The
        Faith" for his book on the seven sacraments against Luther.
              Leo undoubtedly misjudged the seriousness of what was happening,
        and was preoccupied by Medici concerns. Pope Leo lived to see the
        French driven from Milan on 19 November 1521, but was to die suddenly
        of malaria on 1 December 1521.
 

Source: Leo van de Pas