Columbia subject headings:
Fortification--Germany--Saarlouis--Congresses.
Hygiene--Germany--Saarlouis--Congresses.
Water-supply--Germany--Saarlouis--Congresses.
Harvard subject headings:
Fortification--Europe--Congresses.
Fortification--Europe--Water-supply--Congresses.
Hygiene--Europe--Congresses.
Water-supply--Europe--Congresses.
Princeton subject headings:
Fortification--Germany--Saarlouis--Congresses.
Hygiene--Germany--Saarlouis--Congresses.
Water-supply--Germany--Saarlouis--Congresses.