San Ildefonso. The United States took formal possession of New Orleans on December 20, 1803, and of Upper Louisiana on March 10, 1804. John Carroll, the Bishop of Baltimore, served as apostolic administrator of the diocese from 1805 to 1812. The diocese became a suffragan of the see of Baltimore, which had been elevated to a metropolitan archdiocese in 1808, during this period. Archbishop Carroll's successor as apostolic administrator would eventually be the diocese's first resident bishop of the 19th century. In 1823, Pope Pius VII appointed Joseph Rosati to the office of coadjutor bishop of the diocese. At the diocesan bishop's suggestion, the diocesan bishop was based in New Orleans while his coadjutor was based in St. Louis. On 19 August 1825, Pope Leo XII erected the Apostolic Vicariate of Alabama and the Floridas, taking its territory from the Roman Catholic Archdiocese of Louisiana and the Two Floridas. Although the two Florida territories were no longer part of the diocese, he did not change its title. But soon after, Bishop Rosati abruptly resigned the office of coadjutor bishop during a trip to Rome after which the Vatican decided to split the diocese again, making St. Louis a separate see. On 18 July 1826, the same pope Erected the Diocese of St. Louis, taking its territory from the Diocese of Louisiana and the Two Floridas and the Diocese of Durango, Erected the Apostolic Vicariate of Mississippi, taking its territory from the Diocese of Louisiana and the Two Floridas, Changed the title of the Diocese of Louisiana and the Two Floridas to Diocese of New Orleans, and Appointed Bishop Rosati as apostolic administrator of both the Diocese of New Orleans and the new Diocese of St. Louis. On 19 July 1850, Pope Pius IX erected the Apostolic Vicariate of the Indian Territory East of the Rocky Mountains. On the same day, he elevated the Diocese of New Orleans to a metropolitan archdiocese. On 29 July 1953, Pope Pius IX erected the Diocese of Natchitoches, taking its territory from the archdiocese and making it a suffragan of the same metropolitan see. On 11 January 1918, Pope Benedict XV erected the Diocese of Lafayette in Louisiana, taking its territory from the archdiocese making it a suffragan of the same metropolitan see. On 22 July 1961, Pope John XXIII erected the Diocese of Baton Rouge, taking its territory from the archdiocese and making it