Columbia subject headings:
Cities and towns--Russia (Federation)--Volga River Region--History.
Excavations (Archaeology)--Russia (Federation)--Volga River Region.
Fortification--Russia (Federation)--Volga River Region--History.
Harvard subject headings:
Bulgars (Turkic people)--History, Military.
Fortification--Russia (Federation)--Volga River Region.
Princeton subject headings:
Cities and towns--Russia (Federation)--Volga River Region--History.
Excavations (Archaeology)--Russia (Federation)--Volga River Region.
Fortification--Russia (Federation)--Volga River Region--History.