The picture below shows a retaining wall. It was hard to take a picture from a good angle, but it looks to me like the wall is showing a "belly" and the seams are opening up. But I'm not sure: perhaps it was built with these bulges. There's a lot of cement in this wall.
This wall in a Philadelphia suburb and it supports a patio on a very steep decline.
But I do hope that the experts here are able to assess from this picture!