The climate and topography attracted the earliest settlers to what is now present-day Switzerland. The oldest flint tool discovered in Switzerland (an isolated find) is thought to be around 400,000 years old, while more explicit evidence of human activity dates back about 120,000 years. The oldest known agricultural and pastoral settlements in Switzerland date from between 5500 and 5000 BC and bear witness to the transition of these people from a nomadic to a sedentary lifestyle. Some of the most interesting archaeological finds are those of the lakeside settlements dating back to the end of the 5th millennium BC, which have been discovered in the region between Lake Geneva and Lake Constance.
From the early 3rd century BC, the territory of present-day Switzerland was gradually absorbed into the Roman Empire. However, Switzerland was not a single political unit but was divided between five different Roman provinces. The Romans tightened their grip on the territory by establishing colonies. The indigenous population, which included the Celtic Helvetians and the Raetians, became increasingly Romanised. The fall of the Western Roman Empire led to the collapse of the Roman administration in the 5th and 6th century AD.