In defensive terms, no, not really. They had to build it like this because these aren’t really walls per se, it’s just brick lining on the outside of an earthen mound, and mounds are, well, mound-shaped. https://gomadnomad.com/wp-content/uploads/2013/02/Bukharas-Ark-Palace.jpg

So it doesn’t fall down

Is it a lean, or is it wider at the bottom?

Not this one, but newer forts were built with angled walls to help protect against canon balls and the like.

Harder to knock down or undermine?

You’d think it would lean the other way to make bit harder to climb.

Edit: or this could be a view from the inside. Or maybe the goal is to keep people in rather than out.

Edit again: none of these things seem true according to Wikipedia. It’s curved inwards and it houses the rich, so it seems to just be aesthetics.

Are we sure they built it like that 1500 years ago? Churches can suck down in the span of only a few hundred years.

Well clearly it’s because the castle defenders of that era were quite sophisticated, but simply don’t dance they just pull up their pants and do the rockaway.

Harder to get on the wall would be my guess

It’s gregnant