Getting your army across a bridge to confront a defender can be quite difficult. Here are some steps to approaching this situation that should help you emerge victorious:

• If you have cavalry units, place them in a loose formation and use their speed to get across quickly and gain a foothold on the other side.
• Move your archers and other ranged units to the banks of the river near the bridge.
• Use the archers to rain arrows down on enemy units which come to defend the bridges.
• If you were not able to get cavalry across the bridge, use inexpensive units such as Yari Ashigaru to begin crossing the bridge.
• When enemy units move forward to counter your troops on the bridge immediately withdraw them.  Have your archers attack the enemy as he approaches.
• Repeat these steps until you have whittled the opposing force down enough to allow you to begin to move your army across.

Keep in mind:

1. Always send your most mobile troops across the bridge first. They have a better chance of quickly gaining a foothold so that others may pass.
2. You can set your archers to "fire at will" when the enemy approaches the bridge. They will select the best targets automatically.