These measures, by which the caliph hoped to satisfy the ambitions of his sons, did not have the desired effect. Despite the immense concessions he had received, el-Muntasir, anxious to commence his rule over the whole of the Islam empire, secretly conspired against his father and meditated taking his life. Finding that in Egypt he was too far from the scene of his intrigues, he deputed the government of that country to Yazid ibn Abd Allah, and returned to his father's court to encourage the malcontents and weave fresh plots. His evil schemes soon began to bear fruit, for, in the year 244 of the Hegira, his agents stirred up the Turkish soldiery at Damascus to insurrection on the ground of deferred payment. Whereupon the caliph paid them the arrears, and left Damascus to retire to Samarrah. [Illustration: 356.jpg THE MOSQUE OF IBN TULUN, CAIRO.] At length, in the year 861 (a.h. 247), Mutawakkil discovered the scarcely concealed treachery of his son, and reproved him publicly. Some days later the caliph was murdered at night by the captain of his Turkish Guard, and Muntasir, who is commonly supposed to have instigated the crime, was immediately proclaimed as his successor in the government. The most important event in Egypt during the reign of Mutawakkil was the falling in of the Nilometer at Fostat. This disaster, was the result of an earthquake of considerable violence, which was felt throughout Syria. The caliph ordered the reconstruction of the Nilometer, which was accomplished the same year, and the Nilometer of the Island of Rhodha was then called Magaz el-jedid, or the New Nilometer. After reigning scarcely a year, Muntasir himself succumbed, most probably to poison, and his cousin Ahmed was elected to the caliphate by the Turkish soldiery, with the title of Mustain. During his brief reign the Moslems were defeated by the Byzantines at Awasia, and in 866 the Turkish soldiers revolted against the caliph and elected his brother Mutazz in his place. Mustain was, however, allowed to retire to Ma'szit. He was permitted to take an attendant with him, and his choice fell upon Ahmed, the son of Tulun, already mentioned. Ahmed served the dethroned prince truly, and had no part in the subsequent murder of this unhappy man.