Crazy siege ballistas

This is not a bug, but a feature. A stupid feature nonetheless.

Recently, my settlement was attacked by Parthia. It started out as a regular assault, except from that it was slingers who was dragging the siege tower.

Suddenly i found my silver shield pikes on my walls under heavy fire from ballista-like arrows. To my surprise, the arrows was fired from the siege tower!
I have never experienced anything like that before, so to me it came as a huge surprise.

But what that was crazy about it, was the fire rate. I mean, the arrows were sent out in pairs, and there was only a couple of seconds between each pair!

That is much faster than a normal ballista.
And after all the Parthians don`t even know how to build a ballista!

yes that can happen, never actually seen the AI do it to me though, not really sieged a lot.

But you can do it to, just click on the unit dragging the tower and chose fire at will.
the ballista will get better and better, that depends on the wall you are assaulting

Aggressive siege tower recipe: 1. Start a siege. 2. Build siege towers. 3. Man the towers and set them on fire at will. 4. Advance! Voila ~;) - you've got towers that attack the defenders, once in range, with ballista missiles!

Regarding the rate of fire - maybe you had those big-big walls that require big-big towers so they act as nasty-nasty repeating balusts?