A much greater danger now threatened Mansur. In the last days of the Omayyads, the Shi‘ites had chosen as caliph, Mahommed b. Abdallah b. Hasan, whom they called the Mahdi and the “pure soul,” and Mansur had been among those who pledged themselves to him by oath. Not unnaturally, the Alids in Medina were indignant at being supplanted by the Abbasids, and Mansur’s chief concern was to get Mahommed into his power. Immediately after his occupying the throne, he named Ziyād b. Obaidallah governor of Medina, with orders to lay hands on Mahommed and his brother Ibrāhīm, who, warned betimes, took refuge in flight. In 758 Mansur, informed that a revolt was in preparation, came himself to Medina and ordered Abdallah to tell him where his sons were. As he could not or would not tell, he together with all his brothers and some other relatives were seized and transported to Irak, where Abdallah and his brother Ali were beheaded and the others imprisoned. Notwithstanding all these precautions, a vast conspiracy was formed. On the same day Mahommed was to raise the standard of revolt in Medina, Ibrāhīm in Baṣra. But the Alids, though not devoid of personal courage, never excelled in politics or in tactics. In a.d. 762 Mahommed took Medina and had himself proclaimed caliph. The governor of Kufa, ‘Isā b. Mūsā, received orders to march against him, entered Arabia, and captured Medina, which, fortified by Mahommed by the same means as the Prophet had employed against the besieging Meccans, could not hold out against the well-trained Khorasanians. Mahommed was defeated and slain. His head was cut off and sent to Mansur. When on the point of death, Mahommed gave the famous sword of the Prophet called Dhu‘l-Fiqār to a merchant to whom he owed 400 dinars. It came later into the possession of Harun al-Rashid. In the meanwhile Ibrāhīm had not only gained possession of Baṣra, Ahwāz and Fārs, but had even occupied Wāsit. The empire of the Abbasids was in great jeopardy. For fifty days Mansur stayed in his room, neither changing his clothes nor allowing himself a moment’s repose. The greater part of his troops were in Rei with his son al-Mahdi, who had conquered Tabaristan, in Africa, with Mahommed b. Ash‘ath, and in Arabia with ‘Īsā b. Mūsā. Had Ibrāhīm marched at once against Kufa he might have crushed Mansur, but he let slip the opportunity. A terrible conflict took place at Bā-Khamra, 48 m. from Kufa. Ḥomaid b. Qaḥṭaba, the commander of Mansur’s army, was defeated, only a small division under ‘Īsā b. Mūsā holding its ground. At that moment Salm, the son of the famous Qotaiba b. Moslim, came to the rescue by attacking the rear of Ibrāhīm. Ḥomaid rallied his troops, and Ibrāhīm was overpowered. At last he fell, pierced by an arrow, and, in spite of the desperate efforts of his followers, his body remained in the hands of the enemy. His head was cut off and brought to Mansur.
Mansur could now give his mind to the founding of the new capital. When the tumult of the Rāwendīs took place he saw clearly that his personal safety was not assured in Hāshimīya,[29] where a riot of the populace could be very dangerous, and his troops were continually exposed to the perverting influence of the fickle and disloyal citizens of Kufa. He had just made choice of the admirable site of the old market-town of Bagdad when the tidings came of the rising of Mahommed in Medina. In those days he saw that he had been very imprudent to denude himself of troops, and decided to keep henceforth always with him a body of 30,000 soldiers. So Bagdad, or properly “the round city” of Mansur, on the western bank of the Tigris, was built as the capital. Strictly it was a huge citadel, in the centre of which was the palace of the caliph and the great mosque. But around this nucleus there soon grew up the great metropolis which was to be the centre of the civilized world as long as the Caliphate lasted.[30] The building lasted three years and was completed in the year 149 (a.d. 766). That year is really the beginning of the new era. “The Omayyads,” says the Spanish writer Ibn Ḥazm, “were an Arabic dynasty; they had no fortified residence, nor citadel; each of them dwelt in his villa, where he lived before becoming caliph; they did not desire that the Moslems should speak to them as slaves to their master, nor kiss the ground before them or their feet; they only gave their care to the appointment of able governors in the provinces of the empire. The Abbasids, on the contrary, were a Persian dynasty, under which the Arab tribal system, as regulated by Omar, fell to pieces; the Persians of Khorasan were the real rulers, and the government became despotic as in the days of Chrosroes.” The reign of Abu‘l-Abbas and the first part of that of Mansur had been almost a continuation of the former period. But now his equals in birth and rank, the Omayyads and the Alids, had been crushed; the principal actors in the great struggle, the leaders of the propaganda and Abu Moslim were out of the way; the caliph stood far above all his subjects; and his only possible antagonists were the members of his own family.
‘Īsā b. Mūsā had been designated, as we have seen, by Abu‘l-Abbas as successor to Mansur. The latter having vainly tried to compel ‘Īsā to renounce his right of succession, in favour of Mansur’s son Mahommed al-Mahdi, produced false witnesses who swore that he had done so. However unwillingly, ‘Īsā was obliged at last to yield, but it was understood that, in case of Mahommed’s death, the succession should return to ‘Īsā. One of the false witnesses was, it is asserted, Khālid b. Barmak, the head of that celebrated family the Barmecides (q.v.), which played so important a part in the reign of Harun al-Rashid. This Khālid, who was descended from an old sacerdotal family in Balkh, and had been one of the trusty supporters of Abu Moslim, Mansur appointed as minister of finance.
A son of Mahommed the Alid had escaped to India, where, with the connivance of the governor Omar b. Hafs Hazarmerd, he had found refuge with an Indian king. Mansur discovered his abode, and caused him to be killed. His infant son was sent to Medina and delivered to his family. Omar Hazarmerd lost his government and received a command in Africa, where he died in 770.
In a.h. 158 (a.d. 775) Mansur undertook a pilgrimage to Mecca, but succumbed to dysentery at the last station on the route. He was about sixty-five years of age, and had reigned for twenty-two years. He was buried at Mecca. He was a man of rare energy and strength of mind. His ambition was boundless and no means, however perfidious, were despised by him. But he was a great statesman and knew how to choose able officers for all places. He was thrifty and anxious to leave to his son a full treasury. He seems to have cherished the ideal that this son, called Mahommed b. Abdallah, after the Prophet, should fulfil the promises of peace and happiness that had been tendered to the believers, and therefore to have called him al-Mahdi. For that purpose it was necessary that he should have the means not only to meet all state expenses, but also to be bounteous. But from the report of the historian Haitham b. ‘Adī[31] about the last discourse which father and son had together, we gather that the former had misgivings in regard to the fulfilment of his wishes.
Khalid b. Barmak took the greatest care of the revenues, but contrived at the same time to consult his own interests. Mansur discovered this in the same year in which he died, and threatened him with death unless he should pay to the treasury three millions of dirhems within three days. Khalid already had so many friends that the sum was brought together with the exception of 30,000 dirhems. At that moment tidings came about a rising in the province of Mosul, and a friend of Khalid said to the caliph that Khalid was the only man capable of putting it down. Thereupon Mansur overlooked the deficiency and gave Khalid the government of Mosul. “And,” said a citizen of that town, “we had such an awe and reverence for Khalid, that he appeased the disorders, almost without punishing anybody.”
3. Reign of Mahdi.—As soon as Mansur was dead, Rabi’, his client and chamberlain, induced all the princes and generals who accompanied the caliph, to take the oath of allegiance to his son Mahommed al-Mahdi, who was then at Bagdad. Isa b. Musa hesitated, but was compelled to give in. In 776 Mahdi constrained him for a large bribe to renounce his right of succession in favour of his sons, Musa and Harun. Mansur wrote in his testament to his son that he had brought together so much money that, even if no revenue should come in for ten years, it would suffice for all the wants of the state. Mahdi, therefore, could afford to be munificent, and in order to make his accession doubly welcome to his subjects, he began by granting a general amnesty to political prisoners. Among these was a certain Ya’qub b. Da’ud, who, having insinuated himself into the confidence of the caliph, especially by discovering the hiding places of certain Alids, was afterwards (in 778) made prime minister. The provincial governors in whom his father had placed confidence, Mahdi superseded by creatures of his own.
In Khorasan many people were discontented. The promises made to them during the war against the Omayyads had not been fulfilled, and the new Mahdi did not answer at all to their ideal. A revolt in 160 under the leadership of a certain Yusuf b. Ibrahïm, surnamed al-Barm, was suppressed by Yazid b. Mazyad, who, after a desperate struggle, defeated Yusuf, took him prisoner and brought him in triumph to Bagdad, where he with several of his officers was killed and crucified. In the following year, Mahdi was menaced by a far more dangerous revolt, led by a sectary, known generally as Mokanna (q.v.), or “the veiled one,” because he always appeared in public wearing a mask. He took up his abode in the Transoxianian province of Kish and Nakhshab, where he gathered around him a great number of adherents. After some successes, the pretender was ultimately cornered at the castle of Sanam near Kish, and took poison together with all the members of his family. His head was cut off and sent to Mahdi in the year 163.
Mahdi had been scarcely a year on the throne when he resolved to accomplish the pilgrimage to Mecca. The chroniclers relate that on this occasion for the first time camels loaded with ice for the use of the caliph came to Mecca. Immediately on his arrival in the Holy City he applied himself, at the request of the inhabitants, to the renewal of the curtains which covered the exterior walls of the Ka‘ba. For a very long time no care had been taken to remove the old covering when a new one was put on; and the accumulated weight caused uneasiness respecting the stability of the walls. Mahdi caused the house to be entirely stripped and anointed with perfumes, and covered the walls again with a single cloth of great richness. The temple itself was enlarged and restored. On this occasion he distributed considerable largesses among the Meccans. From Mecca Mahdi went to Medina, where he caused the mosque to be enlarged, and where a similar distribution of gifts took place. During his stay in that city he formed for himself a guard of honour, composed of 500 descendants of the Ansār,[32] to whom he assigned a quarter in Bagdad, named after them the Qatī‘a (Fief) of the Ansār. Struck by the difficulties of every kind which had to be encountered by poor pilgrims to Mecca from Bagdad and its neighbourhood, he ordered Yaqtīn, his freedman, to renew the milestones, to repair the old reservoirs, and to dig wells and construct cisterns at every station of the road where they were missing. He also had new inns built and decayed ones repaired. Yaqtīn remained inspector of the road till 767.
During the reign of Mansur the annual raids against the Byzantines had taken place almost without intermission, but the only feat of importance had been the conquest of Laodicea, called “the burnt” (ἡ κατακεκαυμένη), by Ma‘yūf b. Yahyā in the year 770. At first the armies of Mahdi were not successful. The Greeks even conquered Marash (Germanicia) and annihilated the Moslem army sent from Dābiq. In 778, however, Hasan b. Qaḥṭaba made a victorious raid as far as Adhrūliya (Dorylaeum); it was on his proposition that Mahdi resolved on building the frontier town called Ḥadath (Adata), which became an outpost. In 779 the caliph decided on leading his army in person. He assembled his army in the plains of Baradān north of Bagdad and began his march in the early spring of 780, taking with him his second son Hārūn, and leaving his elder son Mūsā as his lieutenant in Bagdad. Traversing Mesopotamia and Syria, he entered Cilicia, and established himself on the banks of the Jihan (Pyramus). Thence he despatched an expeditionary force, nominally under the command of Hārūn, but in reality under that of his tutor, the Barmecide Yahyā b. Khālid. Hārūn captured the fortress Samālu after a siege of thirty-eight days, the inhabitants surrendering on condition that they should not be killed or separated from one another. The caliph kept faith with them, and settled them in Bagdad, where they built a monastery called after their native place. In consequence of this feat, Mahdi made Hārūn governor of the whole western part of the empire, including Azerbaijan and Armenia. Two years later war broke out afresh between the Moslems and the Greeks. Leo IV., the East Roman emperor, had recently died, leaving the crown to Constantine VI. This prince being only ten years old, his mother Irene acted as regent and assumed the title Augusta. By her orders an army of 90,000 men, under the command of Michael Lachanodrakon, entered Asia Minor. The Moslems, on their side, invaded Cilicia under the orders of Abdalkabīr who, being afraid of encountering the enemy, retired with his troops. Irritated by this failure, the caliph in 781 sent Hārūn, accompanied by his chamberlain Rabī’, 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 Hārūn’s general, Yazid b. Mazyad, and put to flight. Hārūn 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 Hārūn that he appointed him successor-designate after Mūsā and named him al-Rashīd (“the follower of the right cause”). Three years later, he resolved even to give to him the precedence in the succession instead of Mūsā, yielding to the importunity of Khaizorān, the mother of the two princes, and to his own predilection. It was necessary first to obtain from Mūsā a renunciation of his rights; and for that purpose he was recalled from Jorjān, where he was engaged on an expedition against the rebels of Tabaristān. Mūsā, 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 Māsabadhān, 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 Mūsā of having been concerned in it, but of this we have no proof whatever.