Iranian and Arab merchants were among the first long-distance traders who sailed from the Persian Gulf to China. Many settled in Guangzhou or other coastal cities, establishing diaspora communities in an efficient maritime trade network, at a time when Chinese merchants were not yet actively sailing overseas. Here, I collect and comparatively analyze both textual and archaeological sources to reassess the role of Iranian and Arab merchants in initiating China's expansion of long-distance overseas maritime commerce. Local kilns, for example, were already producing ceramics for Middle Eastern markets during the Tang. I also show evidence that attests to a much more active role of the Tang court in Sino-Arab relations than has hitherto been assumed. But corruption in local management of maritime trade and political conflicts also had far-reaching consequences on the presence of Iranian and Arab merchants in Guangzhou and the functioning of their networks.