Cannondrum

The enemy will not approach any closer to the towering walls of stone.
They remain just beyond the range of cannons and are assembling what appears to be some new form of siege engine unlike anything before devised. Confident of the citadels' defenses, and the inability of any army to breach these walls in the past, you wonder why they even bother as you climb the parapet for an unobstructed view.

For eight days now the enemy has been stripping bare the small copse of Cedar between the keep and the river, peeling and stripping timbers while their Smiths fashion brackets and couplings and strangely enough scores of tailors frantically stitch together animal hides. Only today have they begun to assemble the framework they've constructed.
It is much more massive than any siege tower or engine that you have ever heard of and looks completely useless for the storming of a fortress. Quickly now the shape of their design begins to reveal itself. A massive series of hoops, five...maybe six stories tall, which they begin connecting and cross bracing to create a shallow cylinder which faces the keep.

"If they are planning on rolling that contraption down on us, they've got it turned the wrong way." you mutter to your replacement as you head for the sentry barracks. Tomorrow should bring a bit more of an idea as to what they have in mind.

The first light of false dawn is heralded by three blasts of the alarm horn. They must be mobilizing you think, as you hastily don uniform and race for the wall. The enemy has finished construction some time during the night and you gape in awe as the first chill runs the length of your spine, the first of the "last" few chills ever to do so.

The alarm sounds anew. This time it sounds retreat which, within the confines of the keep, can only mean evacuate the outer wall, but you are as rooted in place as the wall itself, completely immobile and curiously detached as others race past frantically seeking shelter where none can exist. You merely stare vacantly as you watch the enemy align their cannons not towards the citadel but away from it towards the center of what you can now see is the mother of all drums. Although you have never even heard the words parabola or focal point your intuition tells you that the curved inner surface created by the triangular sections of skins will concentrate the sound of those cannons somewhere just inside the outer layer of rock and mortar which the wall you stand on is comprised, and that the small, (in comparison), hole in the center of this drum, allowing the cannon balls to pass harmlessly through it, will do little to lessen the impact.

Torch touches wick and you witness the flash from the first cannon to detonate and see the mighty shock wave soundlessly ripple the trampled grassland between them and you.

The last chill to ever course your spine is cut short.