It is hard to say when these customs were created. But there are many stories which are closely related.
2
登高来避灾去难的习俗由来已久,所以重阳节也叫做登高节。
The custom of ascending a height to avoid epidemics was passed down from long time ago. Therefore, the Double Ninth Festival is also called "Height Ascending Festival".
3
在古代,重阳节人们有登高的习俗。
In ancient time, people used to climb mountains on this day.