In common with the other northern regions, the Aosta Valley was overrun by tribes from north and south, including early Celts and Ligurians. The Romans arrived around 25 BCE and improved links with other regions by building roads and passes through the mountains. However, the Aosta Valley always tried to preserve its independence and traditional culinary customs, which means it is different from the southern parts of Italy. Its cuisine focuses on local ingredients, such as the many cow’s milk cheeses made by cattle farmers in the high mountains. The Aosta Valley joined the Kingdom of Italy in 1861, but has retained its independent status as an autonomous region.