In Western Europe, the 1st millennium BC represents a major pivotal shift for protohistoric societies, as it implied a series of critical cultural and technological changes that ended up with the region crossing the gates of History and integrating the narrative of the classical world. The Mediterranean basin played a crucial role in this process acting as a conveyor of people, technology and ideas between the Levant, the Aegean and the European far West. Indeed, even the rise of the mighty Celtic civilization with the flourishment of Hallstatt and La Tène cultures and the so-called first cities north of the Alps, was to a large degree connected with the development of short and long-distance contact and exchange networks with the Mediterranean World that intensified dramatically during the Early Iron Age (EIA). Especially after the foundation of Massalia at c. 600 BC, new cultural influences spread into the Celtic sphere through the Rhône corridor, reaching inland areas where they merged with autochthonous dynamics and promoted changes in socio-economic systems and land use. Interestingly, a growing body of research has also identified the concurrent rise of major anthropogenic changes in Celtic palaeoenvironments and landscapes. Beyond suggesting a causal relationship between both phenomena, these works highlight the onset of an early phase of heavy anthropization of natural systems since the EIA. This has led to new and specific research questions, such as if the activity of the colonial centres triggered a locally more intensive land use by the natives to release a surplus for commerce, or if it catalysed the development of early urbanism in Western Europe. However, very few studies have openly addressed the environmental/landscape implications of such highly relevant questions in the Celtic world, and thus the impact and role of Greek colonization in the shaping of Western European cultural landscapes remains largely overlooked. This is particularly detrimental since an informed knowledge about European landscapes is an EU priority with strong implications in terms of socio-cultural heritage, land-management and sustainability. CELTMED was designed as a pioneering project aiming to fill in this gap by employing an original and innovative integrated multidisciplinary approach merging palaeoecology and geoarchaeology, in a unique selection of Mediterranean and Celtic Continental sites subject to different degrees of Greek influence. The main goals of the action were to assess 1) if and how the Greek influence over the Celts from the EIA changed men-environment relationships, and promoted specific environmental and landscape changes (new land uses, increased erosion, higher fire activity, silting of wetlands, etc.) in a context of increased pressure on natural resources and emergence of urban phenomena; and 2) if those potential changes differed in time and space between the Mediterranean Celtic sites and the Continental Celtic area with much less Greek influence. In order to provide an adequate long-term perspective, CELTMED’s chronological framework was focused on the whole 1st millennium BC. The goals of CELTMED were designed to provide new relevant concepts and original narratives about the genesis of Western European landscapes and their history, and to improve the knowledge of this shared European heritage. The Gallic site of Lattara in SE France (Lattes), developed from the late VIth c. BC in the Méjean lagoon, provided an ideal ground for action due to its location in one of the rare points of close and prolonged contact between the Celtic and Greek cultures, its unique hybrid nature (as it was a Celtic oppidum with a harbour under Greek control), the very well-known archaeological context, and the abundance of nearby wetlands suitable for palaeoenvironmental studies. CELTMED drilled sedimentary cores from areas where previous work found 1st millennium BC lagoonal sediments close to the site of Lattara, and undertook multi-proxy palaeoecological and geoarchaeological analyses of such sedimentary archives. CELTMED attempted to integrate results obtained in Lattara within the comparative framework of a transmediterranean geographic and cultural transect from the centre of the Greek world in the Aegean, to the hearth of the Celtic sphere in Western Europe. Such transect included two other contemporaneous and culturally different urban sites: 1) Abdera, a wealthy Greek harbour colony founded in the mid-VIIth c. BC in coastal Thrace that owed most of its prosperity to Aegean trade and where direct contact with the natives was limited, providing an image of the genuine landscapes of the Greek world; and 2) Corent, an Iron Age Celtic oppidum in central France developed since the VIth c. BC, and attesting only tenuous contacts with the Mediterranean, representing proper Continental Celtic landscapes. For both sites, CELTMED could build on the results of previous research projects which provided abundant palaeoenvironmental and landscape-evolution datasets for the period of interest. Located in a key geographic and cultural frontier between inland Celtic and Greek worlds, Lattara was a crucial contact area of both civilizations. This transect of coastal to inland sites subject to different degrees of Greek influence represented a unique occasion to explore how the interplay between both cultures from the EIA, each one with different traditions of land and resources management, changed the way Celtic societies interacted with their environments and contributed to the shaping of cultural landscapes in Continental Western Europe.