Ballista and towers.

So, I don't know the exact answer, but here is what I can say about buildings in a city – the answer isn't complete.

In WoG, if you have the Arrow artifact, the damage of towers increases each day while you control the city.
When the owner changes, this tower strength resets and the count starts over. This doesn't happen in SoD.

About the ballista, see here:
/topic/at/107136/