(28 Sept. 1823–10 Feb. 1829)
Of noble parentage, Annibale Sermattei della Genga was born in the Castello della Genga, near Spoleto, on 22 Aug. 1760, was a student in Rome, and after ordination (1783) at the age of not quite 23 became private secretary to Pius VI, who in 1784 sent him as ambassador to Lucerne. Titular archbishop of Tyre in 1793, he was nuncio in Cologne though obliged, because of the French occupation, to reside in Bavaria 1794–1802, being chosen for several diplomatic missions. After returning to Rome he retired to Monticelli near Piacenza until Pius VII sent him as envoy to the diet of Regensburg in 1805, and in 1806 entrusted him with concordat negotiations (in the event unsuccessful) with the courts of Bavaria, Baden, and Württemberg. In 1808 he was in Paris on business with Napoleon, but was coolly received and soon returned. During Pius VII's captivity he lived, effectively a state prisoner, at his abbey of Monticelli but on the pope's restoration in 1814 was sent as nuncio to Paris. Here he fell out with Cardinal Ercole Consalvi (1757–1824), secretary of state, who criticized his failure to negotiate the restitution of Avignon, and retired again to Monticelli. In 1816, however, Pius VII named him cardinal priest of Sta Maria in Trastevere and—with the personal title of archbishop—bishop of Senigallia. Within a few months he resigned the see on grounds of ill health and retired to his residence near Spoleto. In 1820 he became vicar-general of Rome and prefect of several congregations. At the hotly contested conclave of 1823 during which Austria exercised a veto against the favoured candidate, he was elected somewhat against his will by the votes of the zelanti, conservatives with a primarily religious interest who wished a break with the ‘liberal’ Consalvi and a return to more reactionary policies.
A simple, devout man, morally strong but lacking the flair of leadership, Leo shared the wish of the zelanti that his pontificate should have a less political, more religious orientation. As a sign of this he left the Quirinal palace to live at the Vatican. He at once replaced Consalvi with a conservative as secretary of state, appointed a Congregation of State to advise on political and religious matters, and published (May 1825) measures condemning indifferentism, toleration, and Freemasonry, reinforcing the Index and the Holy Office, favouring the Jesuits, and (against the advice of the great powers) announcing a holy year for 1825, which brought tens of thousands to Rome, but very few from outside Italy. His reactionary approach was most evident in dealing with the papal states. Although some of Pius VII's reforms were left intact and useful, if unpopular, fiscal measures introduced, the feudal aristocracy was installed afresh in privileged positions, ecclesiastical courts of the pre-1800 pattern returned, the laicization of the administration was halted, the Roman college was returned to the Jesuits, new chairs were founded at universities but teaching was supervised in ways intended to stifle criticism, and Jews were again restricted to ghettos. The modern state which Consalvi had been tentatively fostering reverted to a police regime infested with spies and intent on stamping out, with penalties ranging from petty clerical surveillance of private life to execution, any possible flicker of revolution. The result was inevitably economic stagnation, the alienation of the middle classes, and hatred for the personally mild pontiff who was held to blame for making the papal state one of the most backward in Europe.