From a short amount of time, I’m not entirely sure how those work. They are connected to the tower the are next to and intended to provide an obstacle for enemies and they work very well. Maybe too well.
In one scenario i was able to kill of 2 (probably normal) catas a group of ~8 people placed in 5-10 minutes and they got the wall only half down while I was often retreating inner. The wall was reinforced, the users may not have used masteries but I think blocking walls, that do not open up towers should may be get nerfed so even a small squad can take them down in a reasonable time. Maybe not get upgraded.