Post Waterloo, fashion started to move away from the simple, “classical” elegance that was the dominant look between 1800-1815. The waistlines stayed above the natural waist, for the most part, but the lines of the dress changed. While still vertical, the skirt doesn't fall quite so naturally from the waistline, and we see the early stages of that lower triangle shape that becomes more pronounced in later years. These two carriage dresses caught my eye while I was browsing, and demanded to be posted. I suspect the green and red number was a knockout in real life.
These plates come from La Belle Assemblée for March 1818. Please click on them to enlarge.