Baron Dealing Heavy Damage Through Pit Wall

I was playing Taliyah and firing Threaded Volleys into the Baron pit across the wall to help my team take it, since I had walked behind the wall to ward. I noticed that I was taking damage, presumably from Baron since no-one was around, and lost almost half my health in about ten seconds.

This has never happened to me before. I can’t find anything on the Wiki to explain it. I think it must be the recent Baron buffs.