Bridges & Fords
If there is a bridge or ford crossing a river on the campaign map, and an army is standing on it when they are attacked, the resulting battle will occur at the crossing, so the battlefield will feature the river and at least one bridge or ford. Remember if you are the defender that you may have to defend two crossings, or the second one could be used to your advantage.
Attacking a River Crossing
When attacking across a river, try to soften up the enemy on the far bank by bombarding them with missiles first. Once they are weakened, your assault has a better chance of succeeding.
Defending a River Crossing
When defending a river crossing it may be best to stand back in order to stay out of range of enemy missile troops. When their main force starts to cross, rush a couple of units up to stop them. Also be wary of multiple crossings.