Cardinal-bishop of Ostia

The Bishop of Ostia is the head of the suburbicarian diocese of Ostia, one of the seven suburbicarian sees of Rome. The position is now attached to the post of Dean of the College of Cardinals, as it has been since 1150, with the actual governance of the diocese entrusted to the Vicar General of Rome.

Ostia and Velletri, "Ostia e Velletri" in Italian, was a single suburbicarian diocese from 1105 to 1914. In 1914, Velletri (now Velletri-Segni) was split off as a separate suburbicarian diocese. Starting then, a new Dean would add the see of Ostia to the suburbicarian see he already had.

(actually in control of Ostia)

(after 1415 restricted to Peñíscola)

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Wikipedia