Suburbicarian diocese

The seven suburbicarian dioceses are Roman Catholic dioceses located in the suburbs that surround Rome, reserved for the highest order of Cardinals. A Cardinal Bishop is named titular bishop of each of the sees, which have varied slightly in history but are now Velletri-Segni, Porto-Santa Rufina, Frascati, Palestrina, Albano, Sabina-Poggio Mirteto, and Ostia; the see of Ostia is conferred on the Dean of the College of Cardinals in addition to his other see; the Dean is chosen by and from the six cardinal bishops of the suburbicarian dioceses, with the approval of the pope (formerly the dean was always the longest-serving cardinal bishop). However, since the 1960s, six of the dioceses have had their own substantive bishop, pursuant to a decree of Pope John XXIII titled Suburbicarii Sedis, with the exception of Ostia which was merged with the diocese of Rome and is administered by Rome's Cardinal Vicar General.

The titular bishops still formally "take possession" of the dioceses but the substantive bishops exercise all ordinary jurisdiction.

List of Cardinal-Bishops of Ostia