The annual tributes, customs, and direct taxation of the provinces, tended still further to produce the balance of values. The farmers were paid with their own money. The Romans laid not only heavy duties upon the natural products of every country subject to their sway, but also an export duty on produce sent away, as well as an import duty on any article brought in for the consumption of the provinces. A transit duty was even levied on goods and produce of British origin during their passage through the Roman province of Gaul. At the other extremity of the empire, on the coasts of the Arabian Gulf, the same system of fixed taxation was enforced; but the high prices we have named as prevailing at Rome for foreign goods of all kinds, especially those of India, Arabia, and Babylonia, rendered this taxation comparatively light. The _Portorium_[305] or tax on produce or manufactures brought by sea, resembled greatly the custom duties levied at the ports of Great Britain during the present century; they were exacted by officers of the public revenue, at harbours, rivers, and sometimes also at the passages of bridges. On the other hand, besides the relief from municipal taxation, an adequate and regular supply of corn was deemed so essential that shipowners were offered liberal bounties to bring it from abroad. In the reign of Tiberius, it is stated by Tacitus,[306] that, as the people murmured at the oppressive price of grain, the emperor settled its price to the buyer, and undertook to pay two sesterces a measure to the corn-dealers and importers. More than this, the Emperor Claudius, unlike the rulers of some of the nations of our own time, whose systems are too often prohibitory of the importation of the staple article of food for the people, urged the ship-owners to make voyages during the winter, when they usually laid up their vessels, and besides confirming to them the allowances sanctioned by Tiberius, with relief from municipal taxation, took on himself all losses, at the same time securing the importers a certain rate of profit. [Sidenote: System of collecting the taxes.] [Sidenote: A.D. 211.] [Sidenote: Value of the trade with Alexandria.]