Please answer a question about the following article about Alps:

Celtic tribes settled in Switzerland between 1000 to 1500 BC. The Raetians lived in the eastern regions, while the west was occupied by the Helvetii and the Allobrogi settled in the Rhone valley and in Savoy. Among the many substances Celtic tribes mined was salt in areas such as Salzburg in Austria where evidence of the Hallstatt culture was found by a mine manager in the 19th century. By the 6th century BC the La Tène culture was well established in the region, and became known for high quality decorated weapons and jewelry. The Celts were the most widespread of the mountain tribes—they had warriors that were strong, tall and fair skinned skilled with iron weapons, which gave them an advantage in warfare.

When did Celtic tribes settle in Switzerland?
between 1000 to 1500 BC