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.