A testimony from Pope Gregory the Great (590-604) attests to the existence of the diocese in the year 601; prior to this date, no positive documents are found regarding its origins, nor those of the other coexisting bishoprics. Until the 11th century, Ajaccio, like all the dioceses of Corsica, was directly dependent on the Holy See. However, in 1077 Gregory VII appointed the bishop of Pisa as governor of the island, and Urban II elevated him to the dignity of archbishop of Corsica with the bull dated 22 April 1092. Nevertheless, in order to restore peace between the republics of Genoa and Pisa, Innocent II, with the bull *Iustus Dominus* of 19 March 1133, assigned to the former, as suffragans, the bishoprics of Mariana, Nebbio, and Accia; as for Ajaccio, he left it under the jurisdiction of Pisa, along with Aleria and Sagona. It seems that this arrangement underwent no ecclesiastical modification when the entire island passed under Genoese domination. But after that republic ceded Corsica to France (1769), the Pope, in turn, granted to the Most Christian King, at least from 1772 onward, the faculty of appointing the bishops of the island.
The Concordat of 1801 reduced the bishoprics to a single one, with its see at Ajaccio, which became a suffragan of Aix; for this reason, the present diocese of Ajaccio comprises the territory of the six ancient bishoprics of Corsica, namely: ACACIA (v.), Aleria, Mariana or Bastia, Nebbio or San Fiorenzo, Sagona or Vico, and ancient Ajaccio.
It has 220 diocesan priests and 75 regulars, including Dominicans, Franciscans, Capuchins, Oblates of Mary Immaculate, and others, serving a population of 180,000 inhabitants, distributed across 450 parishes. At Lavasina, near Bastia, is the most important sanctuary of the island, dedicated to Our Lady of Graces and declared a national monument. The sanctuary, run by the Franciscans, is annually, especially on 8 September, the destination of numerous pilgrimages coming from all parts of Corsica.