Ibn Alkami, like Nassireddin, swore vengeance against the khalif: he had to complain, not only of the neglect of some of the grandees and favourites being unpunished by Mostassem, but also, he feared for his own personal security, on account of some severe measures against the Shiites, to which sect he himself belonged. He entered, therefore, on the same path of treachery, in which Nassireddin had already preceded him, and besieged the ear of Hulaku, with complaints and invitations, which were readily accepted. Nassireddin, Hulaku’s vizier, and Ibn Alkami, the khalif’s, played mutually into each other’s hands. The contemporaneous fall of two such powerful sovereignties, as that of the Assassins and of the khalifat, caused by the jealousy and treachery of an astronomer and a wit, is unique in history.[265] Ere we commence the detail of the fall of the khalif throne of Bagdad, it will be proper to premise a few words, relating to the foundation and splendour of this renowned city. Bagdad, the city, valley, or house of peace, the citadel of the holy, the seat of the khalifat, called also the oblique,[266] from the oblique position of its gates, was founded, on the banks of the Tigris, in the 148th year of the Hegira, by Abujafer Almansur, the second khalif of the Abbas family. It stretches two miles along the eastern banks of the river, in the form of a bow with an arrow on the string, and is surrounded by a brick wall, whose circumference of twelve thousand four hundred ells, is interrupted by four gates and one hundred and sixty-three turrets. When Mansur resolved upon building the city, he called his astronomers, at whose head was his vizier, Nevbakht (i. e. _new fortune_), to determine a fortunate hour for laying the foundations; and the latter chose a moment when the sun stood in the sign Sagittarius, by which the new city was promised flourishing civilization, numerous population, and long endurance. At the same time he assured the khalif, that neither he, nor any of his successors, would die within the walls of this capital; and the confidence of the astronomer, in the truth of his prophecy, is less surprising than its fulfilment by thirty-seven khalifs, the last of whom, Mostassem, during whose reign Bagdad fell, did not die within its walls, but at Samara, a place built below Bagdad, on the banks of the Tigris, by Motassem, the eighth Abbaside khalif (called the eighther from the coincidence of the number eight, in his nativity) for his Mameluke guard.[267]