 In medieval times the diocese extended from the Aar, near Solothurn, to the northern end of the Valley of St. Imier, thence along the Doubs and the ridge of the Jura Mountains to where the Aubonne flows into Lake Geneva, and thence along the north of the lake to Villeneuve whence the boundary-line followed the watershed between Rhône and Aar to the Grimsel, and down the Aar to Attiswil.Thus the diocese included the town of Solothurn and part of its territory that part of the Canton of Berne which lay on the left bank of the River Aar, also Biel/Bienne, the Valley of St. Imier, Jougne and Les Longevilles in the Franche-Comté, the countships of Neuchâtel and Valangin, the greater part of the Canton of Vaud, the Canton of Fribourg, the countship of Gruyère and most of the Bernese Oberland.The present Diocese of Lausanne includes the Cantons of Fribourg, Vaud and Neuchâtel.