Vatican City.
In Catholicism, the city that is a stronghold in France is Paris.
Roman Catholicism is centered (if by centered you mean that the head of Roman Catholicism, the Pope, lives there) in Vatican City, an independent city-state surrounded by Rome.
No, is a global religion.
Vatican City, an independent city-state within Rome, Italy is the center of Roman Catholicism.
Vatican City is the center of Catholicism.
Vicksburg, Mississippi
Granada was the last city to be Moorish territory.
Vicksburg, Mississippi
Vicksburg, Mississippi
King David established the city of Jerusalem as his stronghold
Stronghold of security
The Catholic religion is in every country. As far as I know, the only country whose only religion is Catholicism is Vatican City.