Discovery, Exploration
As explorers increasingly got higher and higher in the wall, so too did the deadlyness of the monsters they found. As such many groups chose to simply stay in the lower part of the wall where they made a living for themselves.
As groups of explorers gave up on getting to the top they looked for other means of getting money from exploring the wall. This came in the form of an adventurer, who had gotten wounded from a fight early on, and decided to split off from his group and head down. On the way down he had taken extra time to examine a few crevasses and had found rare plants with healing properties. This newfound treasure was something a lot of people were looking for and increasingly more of it was found as explorers started searching for it. Shortly after the discovery groups would enter the wall simply to get more of these herbs along with whatever other plants could be sold.