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