Columbia subject headings:
Arabian Peninsula--History.
Caliphs.
Hārūn al-Rashīd, Caliph, approximately 763-809.
Harvard subject headings:
Caliphs.
Hārūn al-Rashīd, Caliph, approximately 763-809.
Islamic Empire--History--750-1258.
Princeton subject headings:
Arabian Peninsula--History.
Caliphs.
Hārūn al-Rashīd, Caliph, approximately 763-809.