under the orders of Abdalkabir who, being
afraid of encountering the enemy, retired with his troops. Irritated by
this failure, the caliph in 781 sent Harun, accompanied by his
chamberlain Rabi', with an army of nearly 100,000 men, with orders to
carry the war to the very gates of Constantinople. The patrician
Nicetas, count of Opsikion, who sought to oppose his march, was defeated
by Harun's general, Yazid b. Mazyad, and put to flight. Harun then
marched against Nicomedia, where he vanquished the domesticus, the chief
commander of the Greek forces, and pitched his camp on the shores of the
Bosporus. Irene took alarm, sued for peace, and obtained a truce for
three years, but only on the humiliating terms of paying an annual
tribute of 90,000 denarii, and supplying the Moslems with guides and
markets on their way home. This brilliant success so increased Mahdi's
affection for Harun that he appointed him successor-designate after Musa
and named him _al-Rashid_ ("the follower of the right cause"). Three
years later, he resolved even to give to him the precedence in the
succession instead of Musa, yielding to the importunity of Khaizoran,
the mother of the two princes, and to his own predilection. It was
necessary first to obtain from Musa a renunciation of his rights; and
for that purpose he was recalled from Jorjan, where he was engaged on an
expedition against the rebels of Tabaristan. Musa, informed of his
father's intentions, refused to obey this order, and Mahdi determined to
march in person against him. But, after his arrival at Masabadhan, a
place in Jabal (Media, the later Persian Irak), he died suddenly, at the
age of only forty-three. Some attribute his death to an accident met
with in hunting; others believe him to have been poisoned. Some European
scholars have suspected Musa of having been concerned in it, but of this
we have no proof whatever.

The reign of Mahdi was a time of great prosperity. Much was done for the
organization of the huge empire; agriculture and commerce flourished;
the revenues were increasing, whilst the people fared well. The power of
the state was acknowledged even in the far east: the emperor of China,
the king of Tibet, and many Indian princes concluded treaties with the
caliph. He was an ardent champion of the orthodox faith, repudiating all
the extravagant doctrine preached by the Abbasid missionaries and
formerly professed by his father. In particular he persecuted
mercilessly the