After the death of al-Mughira in 670, Kufa and its dependencies were attached to Ziyad's governorship, making him the practical viceroy over Iraq and the eastern half of the Caliphate. He was the first to serve as the dual governor of Kufa and Basra and divided his residence between the two towns. In the winter he stayed in Basra and left
Amr ibn Hurayth as his deputy in Kufa, while he resided in Kufa in the summer, leaving
Samura ibn Jundab as his deputy in Basra. His strong grip in Kufa marked a shift from al-Mughira's hands-off approach. A source of disturbance for him in Kufa was the agitation of the
Alids, partisans of Caliph Ali, led by
Hujr ibn Adi al-Kindi, who disapproved of Umayyad rule and led the first open calls for the caliphate to be held by Ali's progeny. Though al-Mughira tolerated Hujr, Ziyad issued a number of dire warnings to cease his open dissent. He succeeded in turning most of Hujr's supporters among the Kufan troops against him. In 671, he had Hujr and thirteen of his loyalists arrested and sent to Damascus for punishment, where six, including Hujr, were executed in
Adra for their refusal to condemn Ali. One of the men, Abd al-Rahman ibn Hassan al-Anazi, who was spared by Mu'awiya later insulted the caliph after refusing his invocation to condemn Ali and was sent back to Ziyad, who had him buried alive as punishment. To end the chaos in the
amṣar (garrisons) of Basra and Kufa, Ziyad administratively reformed the two towns. From the reign of Caliph Umar, their garrisons consisted of soldiers from different tribes who were grouped together for the distribution of military stipends. There were seven such tribal groups in Kufa and Basra and at the head of each group was a chieftain chosen by its members who served as their representative to the government. Gradually, this system had become economically inefficient and politically turbulent. There was no control on Arab immigration into the
amṣar, resulting in overpopulation and in turn, increased competition over fewer resources. Ziyad thus resolved to form larger divisions by unifying related clans and personally appointing their leader, which resulted in Kufa's reorganization into quarters and Basra into fifths. This measure enabled easier control of the two towns' inhabitants. Ziyad undertook further reforms in Kufa and Basra, including regularizing the timely payment of stipends, embarking on agricultural development schemes, including canal digging, and minting
Sasanian-style dirhams that bore his name as "Ziyad ibn Abi Sufyan".
Consolidation of Khurasan , where Ziyad settled 50,000 Arab troops and their families, and
Balkh and
Tukharistan, where Ziyad's general led expeditions Ziyad's authority extended to
Khurasan and
Sijistan, the far eastern regions of the Caliphate which were considered dependencies of the Basra garrison. The Arab conquests of these areas in the 640s and 650s were akin to raids and did not firmly establish the Caliphate's power. Moreover, the political instability of the final years of Uthman's caliphate and the First Muslim Civil War saw local revolts which further weakened Arab authority. In 655, the Sasanian prince
Peroz III, backed by the army of
Tukharistan, attempted to reassert Persian power. Under previous caliphs, the vast region had been experimentally divided into separate provinces under the leadership of Arab tribal chiefs. Governance was largely left to local princes. Fearing a Persian resurgence, which a fragmentary division of Khurasan could afford, Ziyad centralized the administration of the province in the small Arab garrison at Merv. To relieve Basra's fiscal pressures, Ziyad recommenced the
Muslim conquests in Central Asia. He organized the Arab military presence in Khurasan. In 667, he dispatched an army to the region under his lieutenant general
al-Hakam ibn Amr al-Ghifari. The latter conquered lower Tukharistan and
Gharchistan and temporarily crossed the
Oxus river into
Transoxiana, forcing Peroz to withdraw into
Tang China. Meanwhile, Ziyad's removal of dead soldiers and input of new recruits to the Iraqi army registers led to numerous tribesmen being taken off the payrolls. He dispatched 50,000 Arab soldiers and their families from Basra and Kufa to permanently settle in the Merv oasis of Khurasan. The resettlement of these troops may have been a means "to defuse possibly dangerous developments" relating to the Arab tribal influx in the two garrison towns, according to the historian
Gerald Hawting. As a result, the Merv oasis became home to the largest concentration of Muslims outside of the
Fertile Crescent. Al-Hakam's successor,
Ghalib ibn Abd Allah al-Laythi, was less successful in subduing Tukharistan and Ziyad sent another of his lieutenants,
Rabi ibn Ziyad al-Harithi, to stamp out the revolts in the conquered areas in 670/71. Rabi proceeded to secure the capitulation of
Balkh, whose inhabitants had revolted against Arab rule, in a treaty and then destroyed the army of the
Hepthalite princes in
Quhistan. In 673, Rabi's son Abd Allah extended Arab rule to the western banks of the Oxus and established tributary agreements with the fortress towns of
Amul and
Zamm. To solidify the territorial gains and supply the manpower for further conquests Ziyad intended for the Arab troops, initially concentrated in the Merv oasis, to colonize other parts of Khurasan. They were ultimately distributed between five regional garrisons under Ziyad's successors. ==Legacy and assessment==