Difficulties in tax collection soon appeared. Egyptian Copts, who had been skilled in tax evasion since Roman times, were able to avoid paying the taxes by entering monasteries, which were initially exempt from taxation, or simply by leaving the district where they were registered. This prompted imposition of taxes on monks and introduction of movement controls. In Iraq, many peasants who had fallen behind with their tax payments, converted to Islam and abandoned their land for Arab garrison cities in hope of escaping taxation. Faced with a decline in agriculture and a treasury shortfall, the governor of Iraq al-Hajjaj forced peasant converts to return to their lands and subjected them to the taxes again, effectively forbidding peasants to convert to Islam. In Khorasan, a similar phenomenon forced the native aristocracy to compensate for the shortfall in tax collection out of their own pockets, and they responded by persecuting peasant converts and imposing heavier taxes on poor Muslims.