Overview
After the battle of Dandanaqan (1040), Tughril took the Iranian plateau and entered Baghdad in 1055, where the caliph named him sultan. That act fixed the pattern of the state: Turkic arms ruling through a Persian administration, with legitimacy conferred by the caliph.
Key developments
Under Alp Arslan and Malik-Shah I, with the great Persian vizier Nizam al-Mulk, the empire reached its height; the victory over Byzantium at Manzikert (1071) opened Anatolia to Turkic settlement and is often seen as a hinge of world history. Nizam al-Mulk wrote the Siyasatnameh, the Book of Government, built the Nizamiyya network of madrasas, and used the iqta system to fund the military from land revenues. He was assassinated in 1092 — per tradition the work of the Assassins, the Nizari Ismailis of Alamut. Persian was the language of court and literature, and the era is marked by Omar Khayyam’s calendar reform (the Jalali calendar, 1079) and by great mosque architecture such as the domes of Isfahan’s Friday Mosque.
End and transition
After Malik-Shah’s death in 1092, succession wars fragmented the empire into regional sultanates and atabeg states. The Iranian line ended in 1194, when Tughril III was killed by the Khwarazmians. They ruled Iran briefly — until the Mongol storm of 1220.