Coastal platforms result from successive episodes of marine modeling and tectonic uplift. When the sea level remains in the same relative position in relation to a rocky mass, the intense activity of the waves creates a planar surface as a result of this abrasion and chemical change. Its preservation is possible due to the drop in sea level, which frees it from the mechanical force of the waves and the seismic activity that normally causes its lifting. The lithostratigraphic units preserved on the Viana do Castelo coast made it possible to date the coastal platforms. This area of the Natural Monument of Alcantilado de Montedor, which corresponds to platform III (of 8 meters), was dated with approximately 235 thousand years.