A section of the Roman aqueduct with its sedimentary filling, supplying water to Geneva between the 1st and the 3rd century was studied using sedimentological, palaeobotanical and mollusc techniques. The results show that the sedimentation started when the water-main was still active. The upper part of the sediment consists of local material brought in by the ground water. Historical evidence suggests that the aqueduct was out of service at the end of the 3rd century.