landward wall. The Arab and its leaders, whose loyalties were suspect, was deliberately excluded. Imperial expansion Immediately after stabilizing his rule over the former Aghlabid domains, al-Mahdi was virtually obliged to engage in imperial expansion. As Brett puts it, this was ultimately "the goal on which his credibility rested, the conquest of the world to East and West". This meant military operations in three directions at once, against three political and ideological enemies: the Muslim "usurpers", the Abbasids in the east and the Umayyad Emirate of Córdoba in the west; and the main Christian enemy, the Byzantine Empire, in the north, in Sicily and southern Italy. East: Cyrenaica and Egypt Following the consolidation of his rule in Ifriqiya, al-Mahdi's first objective was Egypt, the gateway to Syria and Iraq, the old heartlands of the Islamic world and seat of their Abbasid rivals. The Fatimids hoped for help from their sympathizers in Egypt; not only had al-Mahdi himself stayed at Fustat in 904–905, but the sources record that the local Abbasid governor was forced to execute several people for corresponding with al-Mahdi and his son, al-Qa'im. Conquest of Tripoli The first step east was Tripoli, which submitted to the Fatimids following the fall of the Aghlabid emirate. The local Hawwara Berbers quickly came to resent the overbearing behaviour of the Kutama soldiery, as well as the heavy tax demands placed upon them. A first uprising and siege of Tripoli in 910–911 was followed by a general revolt of the Hawwara in summer 912. The Fatimid governor of Tripoli fled, and all Kutama in the city were slaughtered. Al-Qa'im led a combined land and naval expedition, laying siege to Tripoli until it capitulated in June 913. Al-Qa'im left one of the principal Kutama generals, Habasa ibn Yusuf, there, to prepare the further eastward expansion of the Fatimid empire. Loss of Yemen Al-Mahdi apparently also entertained hopes of a pincer movement against Egypt from two sides, with the support of his missionaries in the Yemen. It was not to be: Ibn al-Fadl, who had conquered most of Yemen from his base in the south of the country, renounced al-Mahdi and proclaimed himself as the in August 911. The reasons for this are unclear, but are likely related to the contemporary processes of disillusionment with al-Mahdi in Ifriqiya, and the news of the execution of Abu Abdallah al-Shi'i. Al-Mahdi had also sent a letter