Switzerland, officially the Swiss Confederation, is a federal republic consisting of 26 cantons, with Bern as the seat of the federal authorities. Switzerland has existed as a state in its present form since the adoption of the Swiss Federal Constitution in 1848. The precursors of Switzerland established a protective alliance at the end of the 13th century (1291), forming a loose confederation of states which persisted for centuries.The oldest traces of hominid existence in Switzerland date back about 150,000 yearsThe oldest known farming settlements in Switzerland, which were found at Gächlingen, have been dated to around 5300 BC. The Old Swiss Confederacy was an alliance among the valley communities of the central Alps. Extending across the north and south side of the Alps in west-central Europe, Switzerland encompasses a great diversity of landscapes and climates on a limited area of 41,285 square kilometres (15,940 sq mi).The population is about 7.9 million, resulting in an average population density of around 190 people per square kilometre (485/sq mi). The more mountainous southern half of the country is far more sparsely populated than the northern half. In the largest Canton of Graubünden, lying entirely in the Alps, population density falls to 27 /km² (70 /sq mi).