Probably more or less the same as with a bridge, I have not found this information anywhere.
There are several task you can perform to destrot the wall.
"To progress to the third stage, servers must break the wall in northern Guzzlemaw Valley. This can be done by blowing horns, desecrating shrines, luring silencers and killing sights of surrender."
Source: tibiafandom
The kill statistics of the worlds that have succeeded suggest approximately 30,000 Frazzlemaws (76%) and 9,500 Silencers (24%) will be slain in building the bridge. The suggested (not proven as it is near impossible to prove) goal is between 100,000 - 150,000 inquisition gold earned across the server. (which are points/gold that you can trade after succeeding in a task)
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