towns were Constantia (Constance) and Arbor Felix (Arbon). After the borders of the Roman Empire were drawn back to the Rhine boundary in the 3rd century BC, the Alemanni gradually settled on the north shore of Lake Constance and, later, on the south bank as well. After the introduction of Christianity, the cultural significance of the region grew as a result of the founding of Reichenau Abbey and the Bishopric of Constance. Under the rule of the Hohenstaufens, Imperial Diets (Reichstage) were held by Lake Constance. In Constance, too, a treaty was drawn up between the Hohenstaufen emperor and the Lombard League. Lake Constance also played an important role as a trading post for goods being traded between German and Italian states. During the Thirty Years' War, there were various conflicts over the control of the region during the Lake War (1632–1648). After the War of the Second Coalition (1798–1802), which also affected the region and during which Austrian and French flotillas operated on Lake Constance, there was a reorganisation of state relationships. Historical maps 1540: the map Lacus Constantiensis by Johannes Zwick and Thomas Blarer shows topographic names, towns and the Rhine. 1555: the map of the route of the Rhine (Rhinelaufkarte) by Caspar Vopel includes a topographical map of Lake Constance with its larger towns, the tributaries and the course of the Rhine. 1633: the Swabian map by Johannes Janssonius, Amsterdam: Totius Sveviae novissima tabula shows Lake Constance with islands, tributaries, towns and villages. 1675: The Lake Constance map, Lacos Acronianus sive Bodamicus, by Nikolaus David Hautt based on Andreas Arzet SJ shows Lake Constance with the adjacent lands. Geography Divisions Lake Constance is located in the foothills of the Alps. The shore length of both main lakes is long. Of this, are located in Germany (Baden-Württemberg , Bavaria ), run through Austria and through Switzerland. If the upper and lower lakes are combined, Lake Constance has a total area of , the third largest lake in Central Europe by area after Lake Balaton () and Lake Geneva (). It is also the second largest by water volume () after Lake Geneva () and extends for over between Bregenz and Stein am Rhein. Its catchment area is around , and reaching as far south as Lago di Lei in Italy. The area of the Obersee, or Upper Lake, is . It extends from Bregenz to Bodman-Ludwigshafen for over