Pius XI (1857-1939) was pope from 1922 to 1939. During his reign the Lateran Treaty between the Vatican and Italy was signed.

Ambrogio Damiano Achille Ratti, who became Pius XI, was born at Desio near Milan, Italy, on May 31, 1857. Ordained a priest in 1879, and having already acquired a name as a brilliant scholar, he devoted most of the subsequent 43 years to work as a Church librarian. He was known as a Latin paleographer and developed new library classification systems. Already known to Benedict XV as a man of exceptional qualities, he was selected by Benedict for diplomatic service and sent as apostolic visitor in 1918 to Poland. The following year he became apostolic nuncio in Poland. He returned to Italy in 1921 and became cardinal archbishop of Milan. He was elected pope on Feb. 6, 1922.

The first crisis facing Pius XI concerned the newly born Fascist movement led by Benito Mussolini. At the...