The human presence in Venice Lagoon dates well before the Roman time. The city of Altinum was one of the focal points of the area and its port was located close to Torcello, today an island in the Venetian lagoon. Several studies report Roman structures and artefacts both on the island and in the canals, as for example the port quay found behind the church of Torcello and the discovery of amphorae on the trade route that connected the port of Torcello with the city of Altinum. Other structures were found in the depth of canals, emerging from the seabed but hidden by the high turbidity of the waters. Th ese structures are particularly interesting also from a biological point of view, since they supply a suitable substratum to sessile organisms otherwise excluded by the depositional environment and fine sediment bottoms of the lagoons. A hidden resolution bathymetric survey was conducted on known underwater archaeological sites to identify suitable points for the settlement of hardsubstrate benthic communities and an extensive ground truthing was carried out through underwater imagery. During this survey, two points of particular interest emerged, as biodiversity hot spots. These sites diff er by tidal and chemical-physical conditions, leading to a characteristic biocoenose different from others found at the bottom of the lagoon canals.
