Jack, it's a great set of photos, and I'm still waiting on the bell tents for my own Dragoon Dio (gotta love those dragoons); however, in all honesty, the bridge per se is a plaster kit that sat in the garage unpainted for many years. It was a leftover from a brief flirtation I had with 1/35 WWII AFV kits and had at one time a Panzer IV sitting on top gathering the dust that would have layered the bridge. I decided to finish the bridge and test water effects before getting serious about making the pontoon bridge dio for Wagram. (I'm really liking "Glass Coat", which is what I've just used on the 'over the top' craters on another manufacterer's site below - minimum shrinkage and crystal hard set).
The surrounds of the bridge are built up from foam offcuts and PVA-based papier mache and then covered with a random and rough application of Megatreat Liquid Sandstone. This product is actually a paving treatment to simulate sandstone and dries quickly to a leathery shell with rough 'stone-like' finish. It can be painted (and dry-highlighted) though it comes in natural sandstone or even a lighter alternative. If you work quickly, you can sprinkle the grass on while it's still wet - or use watery mix of PVA later. The painting is a quick job of drybrush brown and black immersion wash.
So, there you have it - Stone bridges are timeless of course, and can deal with most eras satisfactorily.
Loved your shots. It's the final image that carries the story. Dragoons are always a good story {bravo}}