<P> One economic policy of Muhammad was a ban on charging fees and rents and a ban on permanent buildings in the market of Medina - only tents were allowed there . This is said to have helped poor traders . </P> <P> The Hawala, an early informal value transfer system, has its origins in classical Islamic law, and is mentioned in texts of Islamic jurisprudence as early as the 8th century . Hawala itself later influenced the development of the agency in common law and in civil laws such as the aval in French law and the avallo in Italian law . The words aval and avallo were themselves derived from Hawala . The transfer of debt, which was "not permissible under Roman law but became widely practiced in medieval Europe, especially in commercial transactions", was due to the large extent of the "trade conducted by the Italian cities with the Muslim world in the Middle Ages ." The agency was also "an institution unknown to Roman law" as no "individual could conclude a binding contract on behalf of another as his agent ." In Roman law, the "contractor himself was considered the party to the contract and it took a second contract between the person who acted on behalf of a principal and the latter in order to transfer the rights and the obligations deriving from the contract to him ." On the other hand, Islamic law and the later common law "had no difficulty in accepting agency as one of its institutions in the field of contracts and of obligations in general ." </P> <P> The waqf in Islamic law, which developed in the medieval Islamic world from the 7th to 9th centuries, bears a notable resemblance to the English trust law . Every waqf was required to have a waqif (founder), mutawillis (trustee), qadi (judge) and beneficiaries . Under both a waqf and a trust, "property is reserved, and its usufruct appropriated, for the benefit of specific individuals, or for a general charitable purpose; the corpus becomes inalienable; estates for life in favor of successive beneficiaries can be created" and "without regard to the law of inheritance or the rights of the heirs; and continuity is secured by the successive appointment of trustees or mutawillis ." </P> <P> The only significant distinction between the Islamic waqf and English trust was "the express or implied reversion of the waqf to charitable purposes when its specific object has ceased to exist", though this difference only applied to the waqf ahli (Islamic family trust) rather than the waqf khairi (devoted to a charitable purpose from its inception). Another difference was the English vesting of "legal estate" over the trust property in the trustee, though the "trustee was still bound to administer that property for the benefit of the beneficiaries ." In this sense, the "role of the English trustee therefore does not differ significantly from that of the mutawalli ." </P>

Upon what type of economic activity were the economies of the islamic empires based