The Eastern and Southern barriers of Buenos Aires originated by a sea-level fluctuation that delivered abundant sand that migrated toward the continent. Using radiocarbon dates performed from material collected below the coastal dunes, three cycles can be achieved. The first cycle originated after the infilling of the estuarine environments (estuaries, coastal lagoons, estuarine lagoons, marshes) approximately 6000 – 4000 years BP depending on sand availability and depth of the estuarine environment. The second cycle of dune formation correspond to a rejuvenation that took place between 3500 and 2400 years BP. The third cycle is younger and it is a reactivation of dunes that took place between 1600 and 500 years BP. These cycles were approximately synchronic with others from the Southern Hemisphere (South Africa, New Zealand and Australia). In modern times, the barrier dynamics was siginificantly altered locally with the fixation, forestation, urbanization and drainage of the dunes, increasing the problems of coastal erosion and groundwater over-explotation and pollution.