It is probable that there were regular officials, under the king's control, who collected dues and looked after the water-transport in the separate sections of the river, or canal, on which they were stationed. It would have been their duty to report any damage or defect in the channel to the king, who would send orders to the local governor that the necessary repairs should be put in hand. One of Hammurabi's letters deals with the blocking of a canal at Erech, about which he had received such reports. The dredging already undertaken had not been thoroughly done, so that the canal had soon silted up again and boats were prevented from reaching the city; in his letter Hammurabi sent pressing orders that the canal was to be rendered navigable within three days.[27] Special regulations were also in force with regard to the respective responsibilities of boat-owners, boatmen and their clients. If a boatman hired a boat from its owner, he was held responsible for it, and had to replace it should it be lost or sunk; but if he refloated it, he had only to pay the owner half its value for the damage it had sustained. Boatmen were also responsible for the safety of goods, such as corn, wool, oil or dates, which they had undertaken to carry for hire, and they had to make good any total loss due to their own carelessness. Collisions between two vessels were also provided for, and should one of the boats have been moored at the time, the boatman of the other vessel had to pay compensation for the boat that was sunk as well as for the lost cargo, the owner of the latter estimating its value upon oath. Many cases in the courts probably arose out of loss or damage to goods in course of transport by water. The commercial activities of Babylon at the time of the First Dynasty led to a considerable growth in the size of the larger cities, which ceased to be merely local centres of distribution and began to engage in commerce farther afield. Between Babylonia and Elam close commercial relations had long been maintained, but Hammurabi's western conquests opened up new markets to the merchants of his capital. The great trade-route up the Euphrates and into Syria was no longer blocked by military outposts and fortifications, placed there in the vain attempt to keep back the invasion of Amorite tribes; and the trade in pottery with Carchemish, of which we have evidence under the later kings of the First Dynasty,[28] is significant of the new relations established between Babylonia and the West. The great merchants were, as a body, members of the upper class, and while they themselves continued to reside in Babylon, they employed traders who carried their goods abroad for them by caravan.