Even a small barrier will slow an advancing army enough to give defending forces the advantage. It’s more difficult to step over obstructions like these when you’re on the march in full armour and if you want to being supply carts, siege engines, etc. through then you’ll have to break a hole in the barrier.
The grass is the obvious issue but what is up what that fence? Why even have one at that point? What are they keeping out? Foliage?
It’s keeping the chlorine gas in, obviously.
Even a small barrier will slow an advancing army enough to give defending forces the advantage. It’s more difficult to step over obstructions like these when you’re on the march in full armour and if you want to being supply carts, siege engines, etc. through then you’ll have to break a hole in the barrier.