Why does the Swiss population speak four languages? What languages are these?

The official languages ​​in the country are:
1) French (20.4% speak it);
2) German (63.7% is used);
3) Italian (6.5% of the population);
4) Retro-Roman (only 0.5%).
The root causes of the linguistic diversity of Switzerland lie in the distant 13th century. The history of Europe is a series of constant endless wars and conflicts for influence, land, resources (however, as in the rest of the world). Especially fiercely fought among themselves kings and emperors in the Middle Ages. The state borders were constantly redrawn in favor of one or another monarch or royal person who was married together with an extensive inheritance in the form of lands.
Tired of such ugliness and the constant transition “from hand to hand”, the inhabitants at the junction of the German, Italian and French borders (then modern Germany, France and Italy did not exist in our usual form) entered into a military alliance and began to be called the “cantons”. Initially, there were three, gradually other lands joined the Federation, the size of the country grew.
In order to take into account the interests of all residents who belonged to different language groups, the authorities gradually developed a system of laws so that no one was offended. So these 4 state languages ​​appeared in Switzerland.