tilia and maple. Population History of settlement Humans began to settle the plateau in the Neolithic, starting with the banks of lakes and rivers. Major oppida were built after the Celts appeared in the 3rd century BC. Urban settlements with stone houses were built during the Roman Empire. The Swiss Plateau became a part of the Roman Empire in 15 BC when the Romans occupied the land of the Helvetii under the reign of Augustus, and it remained Roman until the end of the 3rd century. The most important Roman cities in the Swiss Plateau were Auenticum (today Avenches), Vindonissa (today Windisch), Colonia Iulia Equestris or, by its Celtic name, and Noviodunum (today Nyon). They were well connected by a net of Roman roads. After the retreat of the Roman Empire, the romanized Burgundians occupied the western Swiss Plateau, while the Alamanni settled in the central and eastern portions. The language border between French and German dialects originated in this contrast. During the Middle Ages many towns were founded, especially in the climatically more favoured lower plateau. In 1500 there were already 130 towns, connected by a dense road network. With the rise of industrialisation in the early 19th century, cities became more and more important. In 1860 a drastic population growth of the cities started which lasted for about 100 years. In the 1970s, however, outmigration from the cities started. The municipalities surrounding the cities grew disproportionately, whereas the cities themselves lost inhabitants. In recent times the outmigration has moved farther away from the cities. Today Even though the Swiss Plateau takes only about 30% of the surface of Switzerland, 5 million people live there, which constitutes more than two-thirds of the Swiss population. The population density is 380 people per square kilometre. All the Swiss cities with more than 50 000 inhabitants except Basel and Lugano are situated in the plateau, especially Bern, Geneva, Lausanne and Zurich. The agglomerations of these cities are the most populous areas. Other densely populated areas are located at the south edge next to the Jura, and the agglomerations of Lucerne, Winterthur and St. Gallen. Regions of the higher Swiss Plateau like the Jorat region, the Napf region or the Töss region are comparatively scarcely populated with little farming villages and scattered farms. A majority is German-speaking, though the west is French-speaking. The language border has been stable for many centuries even though