Following the last glacial period the sea level started rising rapidly. The sea started entering the Gulf of Trieste approximately 10000 years ago and since then marine Holocene sediment has been depositing. We wanted to understand how thick this sediment is, so we used modern scientific equipment which lets us determine the depth of the seafloor and the sediment below. The sediment is thickest in the SE part of the gulf (approx. 5 m). In the other parts it is very thin, except near the coast.