Myths, legends and national identities - The national narrative

Switzerland is said to have been born in 1291 with a federal pact that is considered the country's oldest constitutional text. This mythical foundation was celebrated for the first time at the very end of the 19th century. August 1st thus became a national holiday. The choice of August 1st is itself the fruit of political history. Why and how can the past be arranged in favor of a national narrative? What is the nature of myths and what are their functions?