Pop over to flickr and take a look at this picture. Possibly the most innovative design in horse-drawn vehicles I've ever seen (except maybe those German unicycles!!). I imagine that's a pretty heavy vehicle to pull, with all that metal in the construction, though it's not uncommon for large horse-drawn carriages (combined driving vehicles, Amish carraiges, etc.) to weigh many hundreds of pounds. Once the vehicle gets rolling, there's not much effort needed, if it is well balanced. Stopping and starting, or going up and down hills, is where the hard work comes in.