This paper reassesses the political and cultural chronology of northwest Arabia in the second half of the 1st millennium BC. A close review of the available epigraphic and iconographic evidence shows that it cannot provide any firm chronological anchor for the kingdom of Liḥyān nor for the Nabataean takeover of the area: only archaeology may offer new insights into the history of this important but poorly known period. Recent excavation results from Hegra / Madā’in Ṣāliḥ and from various sites in the al-‘Ulā oasis (Dadan / Khuraybah, Tall al-Kathīb, Khīf al-Zahrah) suggest a disruption in the settlement history and the material culture of the area in the 3rd c. BC. At that time, Dadan and its peripheral settlements seem to have entered a phase of decline, while the Iron Age painted pottery tradition probably came to an end. Conversely, the Saudi-French excavations at Hegra show uninterrupted occupation and development throughout the second half of the 1st millennium BC, suggesting that this site had replaced Dadan as a regional centre by the early 2nd c. BC – i.e. well before the commonly accepted date for the Nabataean takeover of the area. Numismatic data confirm the existence of an autonomous power at Hegra from the late 3rd or early 2nd c. through the 1st c. BC, revealing a hitherto unknown chapter in the political and cultural history of northwest Arabia.