The resources of the Romans were principally derived from the tribute levied on the conquered countries; but in part also from duties on merchandize: in the latter point of view, alone, they fall under our notice. No custom duties seem to have been imposed till the time of Augustus; but in his reign, and that of his immediate successors, duties were imposed on every kind of merchandize which was imported into Rome; the rate varied from the eighth to the fortieth part of the value of the article. The most full and minute list of articles of luxury on which custom duties were levied, is to be found in the rescript of the emperors Marcus and Commodus, relating to the goods imported into Egypt from the East. In the preamble to this rescript it is expressly declared, that no blame shall attach to the collectors of the customs, for not informing the merchant of the amount of the custom duties while the goods are in transit; but if the merchant wishes to enter them, the officer is not to lead him into error. The chief and most valuable articles on which, by this rescript, duties were to be levied, were cinnamon, myrrh, pepper, ginger, and aromatics; precious stones; Parthian and Babylonian leather; cottons; silks, raw and manufactured: ebony, ivory, and eunuchs. Till the reign of Justinian, the straits of the Bosphorus and Hellespont were open to the freedom of trade, nothing being prohibited but the exportation of arms for the service of the barbarians: but the avarice, or the profusion of that emperor, stationed at each of the gates of Constantinople a praetor, whose duty it was to levy a duty on all goods brought into the city, while, on the other hand, heavy custom duties were exacted on all vessels and merchandize that entered the harbour. This emperor also exacted in a most rigorous manner, a duty in kind: which, however, had existed long before his time: we allude to the annona, or supply of corn for use of the army and capital. This was a grievous and arbitrary exaction: rendered still more so "by the partial injustice of weights and measures, and the expence and labour of distant carriage." In a time of scarcity, Justinian ordered an extraordinary requisition of corn to be levied on Thrace, Bithynia, and Phrygia; for which the proprietors, (as Gibbon observes,) "after a wearisome journey, and a perilous navigation received so inadequate a compensation, that they would have chosen the alternative of delivering both the corn and price at the doors of their granaries." Having thus given a connected and general view of the Roman commerce, we shall next proceed to investigate the progress of geographical knowledge among them. In our chronological arrangement of this progress, incidental and detached notices respecting their commerce will occur, which, though they could not well be introduced in the general view, yet will serve to render the picture of it more complete.