If you've been in a game store, you've probably seen the river sets available from Gale Force Nine (owned by Battlefront). We recently opened the box on their river bends set. The online catalog includes photos of the river sets being used with Flames of War products.
So, perhaps you're wondering: where are the bridges?
The set arrives in plain packaging, comprising two bridges individually swathed in bubblewrap. They seem to be resin, and come pre-painted.
The stone bridge has two arches, and is built of stones except on the ends (stone bricks/blocks) and the driving surface (some kind of pavement effect). It is 6" long and 2¾" across.
The bottom is painted dark gray. The central support does not come down all the way, leaving space for a river piece beneath.
The other bridge in the set is referred to as the log bridge. The main structure is logs (protruding through the sides) resting on eight log pilings, with overlaid planks providing the road surface. It is 7¾" long and 2⅓" wide.
Again, the bottom is painted dark gray. The four central pilings are raised to accommodate a river piece.
I didn't have any straight Battlefield in a Box river pieces to test these with (hard to find in stock!), but above you see the stone bridge over a river bend piece. Fits perfectly.
The log bridge also fits with the river piece, though in this case it's a tighter fit.
The raised pilings in the center fit perfectly with the river piece.
The bridge also works for 28mm, as you can see with this sci-fi motorcycle. The road is 2⅜" wide.
Would you use this bridge for Ancients? If you prefer cobblestones, there is also a Ruined Bridge in the Battlefield in a Box range – no scale given, same length as this one, but 4" wide.
Here's the same 28mm rider on the log bridge. Looks fine from a distance, but the planks are tiny for 28mm. (Depends how picky you are.) And would you use this log bridge for pre-19th Century?
Note also that our samples differ from the online catalog pictures. The stone bridge online pics show much darker shadowing, with the roadbed being very dark. Meanwhile, the online pics for the log bridge show a two-tone tan bridge, with the roadbed being much lighter.