Do you mean like this?
You could stitch the vertices together with the Line tool and then soften the edges.
You could also use an extension like Curviloft to do the same thing.
It would be better and easier to work with if your arcs top and bottom had the same number of sides and the vertices were aligned.
Here I’ve recreated the lower curve using Offset off the bottom edge of the wall. Then the curves can be stitched together (either manually or via extension) without requiring the triangulation.
There are, of course, other ways to do this which would be more efficient and require less work. For example you could draw the cross section of the wall and use Follow Me to extrude it along an arc path.