In Southeast Asia, archaeological research has recently shown that the earliest centralised polities qualifying as incipient States emerged by the late 5 th and early 4 th c. BCE (Kim 2013; Stark 2015; Bellina 2017; Bellina 2018). Understanding of their hinterland is still very limited. This essay presents the results of a regional study conducted since 2005 in the Isthmus of Kra in the Thai-Malay Peninsula, a narrow piece of land located between the Bay of Bengal and the South China Sea. It argues that in this region, Maritime Silk Road incipient trading states' emergence went along economic specialisation, cultural differentiation and cooperation between different groups participating in local and long-distance networks. Amongst these so-called "marginal" groups emerge "sea nomads". Like those described in historical and ethnographic sources some of which are referred to here, these early sea nomads appeared to have already played a crucial economic and political role as part of these maritime trading polities hinterland. Along with an archaeology of sea nomadism, this study opens perspectives on reconstructing a more complete narrative of Southeast Asia and beyond of the Maritime Silk Road, a narrative that integrates marginal groups.