Columbia subject headings:
Byzantine Empire--Foreign relations--Islamic Empire.
Christianity and other religions--Islam.
Crusades.
Islam--Relations--Christianity.
Islamic Empire--Foreign relations--Byzantine Empire.
Islamic Empire--History.
Harvard subject headings:
Byzantine Empire--Foreign relations--Islamic Empire.
Christianity and other religions--Islam
Crusades.
Islam--Relations--Christianity
Islamic Empire--Foreign relations--Byzantine Empire.
Islamic Empire--History.
Princeton subject headings:
Christianity and other religions--Islam.
Islam--Relations--Christianity.