The descendants of the 'Abid continued to be a powerful military contingent under the reign of Moulay Slimane (r. 1792–1822), but they were no longer the sultan's only pillar of military strength. Slimane took measures to curtail their power, such as recruiting tribal levies (as had been common practice before Isma'il's reign) to act as a counterbalance. Some of the 'Abid continue to hold powerful positions in both central and local government. Meknes continued to be one of their main bases during this period. During the later years of his reign, as he faced mounting rebellions and crises, Slimane sought to revive Isma'il's military policies and to re-enlist the Haratin (free black people) into the army. However, political instability rendered this task difficult and the number of Haratin that were enlisted does not appear to have been significant. Slimane's successor, Abd ar-Rahman, also attempted to re-enlist black soldiers in order to strengthen the military in response to the French conquest of Algeria that began in 1830. The trafficking of slaves also remained vigorous during throughout the early 19th century, and Abd ar-Rahman rebuffed British diplomatic requests to end the slave trade. However, after the defeat at the Battle of Isly (1844) and as contacts with Europe increased over the rest of the century, later 'Alawi sultans attempted to reform the military into a "modern" standing army with salaried soldiers instead of the traditional tribal levies. In the process, the number of black 'Abid soldiers also decreased. Under the reign of Moulay Hassan (r. 1873–1894) only about 5000 of them were still serving in the sultan's standing army, generally as cavalrymen. A French scholar who visited Morocco in the 1880s claimed that this number would increase during times of war. Over time, most of the former 'Abid and their descendants had left the army and gained their freedom. They scattered and resettled across the country. As former slaves, their free status was sometimes questioned, but Moroccan religious scholars generally affirmed that they were free. Some black individuals and families continued to hold powerful positions in the Moroccan government. The most notable example is Ahmad ibn Musa, also known Ba Ahmed, whose family monopolized the office of the sultan's hajib (a chamberlain and vizier) under multiple sultans in the 19th century. Ba Ahmed himself acted as de facto ruler of Morocco during the first four years of the reign of 'Abd al-Aziz