No one can travel over the mountains in winter –

1. because it is so cold that no one can survive
2. because, since there is no food for them at that time, there are no reindeer on the mountains – they are down in the forest
3. because one single reindeer cannot cross them since it is too far
4. because it is not possible to carry enough clothes to keep a man warm nor food to feed him.

Most travelling is therefore done in autumn and summer.