922 the Bulgarians controlled almost the whole Balkan peninsula, but Constantinople remained out of Simeon's reach because he lacked a navy. According to the Byzantine source that reports on these negotiations, al-Mahdi accepted the proposal, but the ship carrying the Bulgarian and Fatimid envoys to Simeon was captured by the Byzantines near the Calabrian coast. When the Byzantine emperor Romanos I learned about the negotiations, the Bulgarians were imprisoned, while the Arab envoys were allowed to return to Mahdiya with rich gifts for the caliph. The Byzantines hastened to renew the 917 peace agreement, including the payment of tribute, and Simeon's death in 927 put an end to his ambitions. Warfare with the Byzantines resumed in 928, when a fleet was sent to Sicily, led by the governor of Kairouan, Sabir al-Fata. He attacked a locality named ('the caves') in Apulia, and proceeded to sack the cities of Taranto and Otranto. The outbreak of a disease forced them to return to Sicily, but then Sabir led his fleet up the Tyrrhenian Sea, forcing Salerno and Naples to ransom themselves with money and precious brocades. In 929, he defeated the local Byzantine on the Adriatic coast, and sacked Termoli. He returned to Mahdiya on 5 September 930, bringing 18,000 prisoners with him. Encouraged by these successes, al-Mahdi planned a new and larger naval offensive against the Byzantines in Italy, but the arrival of a Byzantine embassy led to the conclusion of another truce in 931/2, which was adhered to until after the caliph's death. Legacy Dachraoui attributes to al-Mahdi "tenacity and prudent wisdom" and stresses that, no matter whether al-Mahdi's claims of Alid descent and possession of the imamate were genuine, he was able to successfully establish a new state, end the concealment of the Isma'ili , and "conduct moderate but firm policies within his provinces, and to wage tireless warfare beyond his frontiers". Brett points out that al-Mahdi's emphasis on constructing a state and dealing with the realities of its governance, left him little time to adapt the Isma'ili doctrine to the new situation and "develop this Caliphate of God into a full-blown creed of the Imamate". This was not achieved until the reign of the fourth Fatimid imam-caliph, al-Mu'izz (). It was also left to al-Mu'izz to try and woo over the Qarmatians, the Seveners who after the schism of 899 still expected the messianic return of Muhammad ibn