Columbia subject headings:
Basilica di San Pietro in Vaticano.
Vatican City--Buildings, structures, etc.
Harvard subject headings:
Basilica di San Pietro in Vaticano.
Rome (Italy)--Buildings, structures, etc.
Vatican City--Buildings, structures, etc.
Princeton subject headings:
Basilica di San Pietro in Vaticano.
Church architecture--Vatican City.
Vatican City--Buildings, structures, etc.