The iqtaʿ system was inherited from the Ayyubids and further organized under the Mamluks to fit their military needs. Iqtaʿat were a central component of the Mamluk power structure. The iqtaʿ of the Muslims differed from the European concept of fiefs in that iqtaʿ represented a right to collect revenue from a fixed territory and was accorded to an officer (emir) as income and as a financial source to provision his soldiers. However, prior to the Mamluks' rise, there was a growing tendency of iqtaʿ holders to treat their iqtaʿ as personal property, which they passed down to their descendants. The Mamluks effectively put an end to this tendency, with the exception of some areas, namely in Mount Lebanon, where longtime Druze iqtaʿ holders, who became part of the halqa, were able to resist the abolition of their hereditary iqtaʿat. In the Mamluk era, the iqtaʿ was an emir's principal source of income, and starting in 1337, Mamluk iqtaʿ holders would lease or sell rights to their iqtaʿat to non-mamluks in order to derive greater revenues. By 1343, the practice was common and by 1347, the sale of iqta'at became taxed. The revenues emanating from the iqtaʿ also served as a more stable source of income than other methods the Mamluks sometimes employed, including tax hikes, the sale of administrative posts and extortion of the population. According to historian J. van Steenbergen, The iqtaʿ system was fundamental in assuring a legitimized, controlled and guaranteed access to the resources of the Syro-Egyptian realm to an upper level of Mamluk society that was primarily military in form and organization. As such it was a fundamental feature of Mamluk society, on the one hand giving way to a military hierarchy that crystallized into an even more developed economic hierarchy and that had substantial economic interests in society at large; on the other hand, it deeply characterized the realm's economic and social development, its agriculture, grain trade, and rural demography in particular.