The back has two pleats which are stitched down. I used two full widths for the back and skirt, seaming together at CB. The fronts lap over the back and are stitched down. Skirts use spaced back-stitch used and the pleating. I used 1/4" pleats, but 1/2" are common as well. Notice that the pleats change directions at the pocket slit. You rarely see that on modern reproductions, but it was the most common way to do it historically http://mantuadiary.blogspot.com/search/label/Gown