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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."