The economic dynamics of the twelfth century finds its expression in an increased number of fiscal instruments and terminology. After an introduction to legal taxation and Saljūq fiscal policy, the philological problems of a specific due, al-fissa, illegitimate according to the sharī‘a, will be addressed along with its political function, history, levying and transfer. It was levied in Damascus for an annual and/or occasional tribute to the Kingdom of Jerusalem, even before the alliance of Damascus and Jerusalem in 532/1140. Before Nūr al-Dīn Mahmūd's conquest of Damascus the monies were transferred by bearers of hawālas. It can be suggested that tax farmers were liable for them. A decree, rasm, allowed for the collection of al-fissa. The due was levied perhaps on the basis of an assessment of urban real estate. An interpretation of the term al-fissa was suggested as Arabic borrowing from the middle Latin term fossa.