Tabriz was from the late 1260s the commercial and monetary capital of the Il-Khanid empire, through which the authorities succeeded in routing all significant international commercial traffic passing through Il-Khanid territory. European consumers pulled in more eastern goods than European producers exported to Iran and other eastern destinations. The outlets to the west were the ports of Ayas and Trebizond. The paper investigates the routes by which goods were supplied to Tabriz and the effects of commercial traffic on the cities lying along those routes. The channelling of Indian spices through the port of Hormuz on the Persian Gulf is well known, but the paper will describe Shiraz and Isfahan during the period. The role of Tabriz and Sultaniyya as a clearing-house for Iranian silk, marketed now to the west for the first time, will be described. In a previous period Tabriz had been supplied with Chinese silk and other goods from Central Asia, but this channel now supplied relatively few of the products sold in Tabriz' markets. The principal reason was not (as has been previously thought) that hostility between the Il-Khans and the Chaghatay principality produced conditions inimical to travel, but that Chinese goods were now taken through the Central Asian cities and those of the Golden Horde further west to the port of Tana on the north shore of the Black Sea and from there to the west. The more southerly cities of Central Asia such as Samarkand were correspondingly less active. The silk of Caucasian centres such as Ganja must have been marketed through Tabriz. But Georgian silk may have been transported directly via the still viable and active city of Ani. Finally the existence of Tabriz at one end and of the still commercially active Baghdad at the other end led to the maintenance of a whole swathe of intermediate cities, all supported at some remove by the demand and supply of the two large magnets. The prosperity of individual cities is known. But the explanation is put forward here for the first time. Much reliance is placed on the Latin and Italian sources, whose significance has not always been elucidated, and some on numismatic phenomena. Local Persian and Armenian sources contribute.