2000 ans de colmatage du port antique de Fréjus (Forum Julii, France: une double métamorphose littorale

The ancient harbour of Fréjus, located in a Holocene ria, has been the subject of a research program in archaeology and, notably with regards to the sedimentary environment at its foundation. A core was extracted in the middle of the basin of Fréjus harbour. The objective is to understand the paleogeographical evolution of the pre-harbour and Roman harbour environments. The sedimentological and biostratigraphical proxies enabled us to: (1) confirm Texier's (1849) hypothesis in which the pre-harbour environment comprised a marine bay blocked by an artificial quay (Gébara and Morhange, 2010). Excoffon et al., 2006 and Devillers et al., 2007, demonstrate the presence of a rocky coast (butte Saint-Antoine), at the time of the harbour's foundation, which it has been progressively transformed into a sandy coast due to the sedimentary input of Argens delta. This study permitted: (2) to confirm the date of foundation of Fréjus' harbor; and (3) to show different phases of protection. Indeed, the harbour facies attests to a euryhaline lagoon (B1 and B3) which was gradually transformed into a freshwater lake (B4) due to the progradation of the Argens. Low sedimentation rates (ca. 0.5. mm/year), between the end of the last century BC until seventh century AD is consistent with the dredging of the harbour basin.