Located 90km inland from the Gulf coast, west of modern al-Jubail, Thaj is the largest ancient site known in Eastern Arabia. It was a major hub a long-distance trade in the “Hellenistic” period and in the first centuries AD. It has been known to western scholarship since the beginning of the 20th century, but only limited surveys and excavations have been carried out at the site so far. In 2016, an international archaeological project led by the Saudi Commission for Tourism and National Heritage (SCTH), the CNRS (France) and Leiden University (Netherlands) was launched in order to conduct a comprehensive archaeological exploration of the site, including large-scale excavations and a wide array of specialized studies. The present paper presents the results of the first field season of this project, which took place in Oct/Nov 2016. These first results already shed critical new light on the ancient environment, the plan, the chronology and the material culture of Thaj.