So, I had 56 infantry, 2 artillery, 2 Heavy tanks, 5 Cavalry in a level 5 fort and was attacked by 10 artillery firing from a road. I took damage to the fort and workshop and lost 1 artillery piece. I REMEMBER being inside a level 5 fort and firing artillery with impunity because the fort needed to be taken down before the ones inside being damaged. OH, and just to prove it was not a fluke. I also had 2 artillery inside another level 5 fort and had 3 artillery destroy both artillery pieces with no damage to the infantry and cavalry accompanying them.