Under wise administration Agriculture and Commerce, the twin pillars of national prosperity, necessarily flourished. A scientific canalisation, with irrigation-works inherited from the ancients, made the Mesopotamian Valley a rival of Kemi the Black Land, and rendered cultivation a certainty of profit, not a mere speculation as it must ever be to those who perforce rely upon the fickle rains of Heaven. The remains of extensive mines prove that this source of public wealth was not neglected; navigation laws encouraged transit and traffic; and ordinances for the fisheries aimed at developing a branch of industry which is still backward even during the xixth century. Most substantial encouragement was given to trade and commerce, to manufactures and handicrafts, by the flood of gold which poured in from all parts of earth; by the presence of a splendid and luxurious court, and by the call for new arts and industries which such a civilization would necessitate. The crafts were distributed into guilds and syndicates under their respective chiefs, whom the government did not “govern too much”: these Shahbandars, Mukaddams and Nakíbs regulated the several trades, rewarded the industrious, punished the fraudulent and were personally answerable, as we still see at Cairo, for the conduct of their constituents. Public order, the sine quâ non of stability and progress, was preserved first, by the satisfaction of the lieges who, despite their characteristic turbulence, had few if any grievances; and, secondly, by a well-directed and efficient police, an engine of state-craft which in the West seems most difficult to perfect. In the East, however, the Wali or Chief Commissioner can reckon more or less upon the unsalaried assistance of society: the cities are divided into quarters shut off one from other by night, and every Moslem is expected, by his law and religion, to keep watch upon his neighbours, to report their delinquencies and, if necessary, himself to carry out the penal code. But in difficult cases the guardians of the peace were assisted by a body of private detectives, women as well as men: these were called Tawwábún = the Penitents, because like our Bow-street runners, they had given up an even less respectable calling. Their adventures still delight the vulgar, as did the Newgate Calendar of past generations; and to this class we owe the Tales of Calamity Ahmad, Dalilah the Wily One, Saladin with the three Chiefs of Police (vol. iv. 271), and Al-Malik al-Záhir with the Sixteen Constables (Bresl. Edit. xi. pp. 321–99). Here and in many other places we also see the origin of that “picaresque” literature which arose in Spain and overran Europe; and which begat Le Moyen de Parvenir.[314]