Abu Tahir was the second Nizari da'i in Syria sent by Hassan-i Sabbah, replacing al-Hakim al-Munajjim, and enjoying alliance with Ridwan. He kept using the Nizari base in Aleppo, while continuing the Nizari strategy of seizing strongholds in pro-Isma'ili areas, focusing on the Jabal al-Summaq highlands located between the Orontes River and Aleppo. At this time, the authority over the upper Orontes valley was shared between Janah al-Dawlah of Homs, Munqidhites of Shaizar, and Khalaf ibn Mula'ib, the Fatimid governor of Apamea based in its citadel Qal'at al-Mudhiq.