"Footbridge" is the correct term for a small bridge, the kind that can't be used by carts or vehicles. We have various types and words for bridges but they're structure-related, not size-related. For example, "truss" or "trestle bridge", both related to support systems. Be aware that a "Footbridge" is something that accommodates one or two people abreast at max -probably not something you'll see used by armies in Warbarons?
"Ford" from "Fjord", thanks to our Saxon ancestors, I think. Yeah KGB provided a link but I'm not gonna look