Lousonna, Archaeological site in Lausanne, Switzerland.

Lousonna is a Gallo-Roman vicus in the Vidy district of Lausanne, about 200 m from the north shore of Lake Geneva. The excavated site stretches 1.2 km long and 250 m wide, covering 20 hectares. Visitors can see the forum with its basilica, a schola of the nautae, and a slipway for boats.

Founded around 15 BCE at a crossroads between the Rhône and Rhine basins and on the road to the Great St Bernard Pass, Lousonna grew to 20 hectares and housed 1,500 to 2,000 people at its height. It declined from the 3rd-century Germanic invasions and was abandoned in favour of the Cité hill in the mid-4th century.

The name Lousonna probably comes from a Celtic water goddess honoured as Isis Leusonna, whose name appears on a votive axe found in 1984 in the western house. The boatmen's guild, the nautae lacus lemani, had its meeting hall, a schola, built against the basilica; a 185 cm stone inscription there records a dedication by the nautae.

The site is reachable by regular buses from Lausanne central station and is located near an adjacent museum with exhibits about the excavations. Guided tours can be arranged in advance to help you understand what you are seeing on the ground.

The port and trade system shows how closely connected this place was to Lake Geneva and how goods moved across the water. This connection to water transport was essential to how the community survived and prospered.