The skirmisher cavalry fires a volley into the empire shield wall. Most are able to protect themselves, but two go down.
The cavalry then repositions itself further away from the advancing infantry.
"Deploy field artillery!"
All must do their part. A ballista, crewed by two peasants who were recently trained on how to operate it, enters the field and immediately prepares response fire.
(The ballista is Size 2, with a Size 3 'Gun', giving it a use rating of 5, a range of 14" and 3d6 damage.)
Four soldiers form a phalanx on the bridge.
The Empire - ninja-bait
The imperial spearmen march forward and prepare to throw their spears. They will need to take their actions Over The Top to bridge the range, but with their Officer's Coordination allowing them to roll d8's, they just might.
Most spears fall short, but one kills a skirmisher and another knocks one off his horse and disrupts him.
The Empire's command squad, Sir Jason (Hero) and two bodyguards arrive.
As Sir Godwin expected, water demons appear in the water, ready to attack the barricade. (These guys were gonna be a secret faction but they will be NPC'd.)
A spear is thrown at them and the crossbowmen open fire from the towers, but rolls are low. (The spearman can grab another spear from the barrel next turn.)
The flag on the ground indicates the range of the ballista.