The Greek-Latin authors present Qarthadašt (Cartagena) as one of the main bastions of territorial control of the Carthaginians in Iberia. It had easy and close maritime relationship with Africa, the Strait area and Ibiza, and was located near rich silver deposits. These two reasons are determining factors in its prosperity. The geomorphological evolution and a history without interruption have notably changed the original physiognomy of the site, where the city was founded around 228 BC. This paper focuses on the study of the western sea front of the Cartagena bay. There borehole cores and foundation excavation section allowed to define a strong anthropic action dated at the second half of 3rd century BC. Paleontological (ostracodes and molluskas), geochemical (biomarkers and amino acid racemization) and sedimentological studies allowed to describe a Holocene dated environment with strong continental influence to the north, more marine to the south. Logs and branches sharpened into a point driven into a muddy bottom could be related to a first anthropic activity in the area in a shallow embayment that due to the hydrodynamics change evolved into a thick sand accumulation.