Dave waved his hand again, issuing the command for another volley of trebuchets. The soldiers ignited oil coated boulders and shot them at the enemy ranks. One boulder bore through a siege tower and fell on enemy soldiers squashing them to sludge. The siege tower caught fire and crumbled on the soldiers riding inside it and the ones around it.
Another boulder crashed into a group of soldiers setting them on fire. One man, lit in flames dropped and rolled on the ground. But the fire covering him ignited a trail of black powder mixed with sand that spread until it reached a buried stock of explosive powder kegs. The kegs were coincidently under a siege tower. When the explosive blew up, they lifted the whole siege tower a few feet above the ground, shattering it into burning logs and smoke.
Screams of pain and panic spread among the ranks of the enemy soldiers. They still had no way to deal with the explosives and didn't know where they were planted.