What does The Ark do?

[Glubber]

I am facing two players using undead themes in a current MP game. And even though I am able to fend off most of the attacks, they are slowly whittling me away. I am looking at items to help me fend off these creatures, (yes, I have gobs of priests). So now I am looking at magic items besides Herald Lances.

I am curious, what does the magic item, 'The Ark' do? It says it spreads disease among heretics and you need to have sacred troops to use it to be immune. But does it have shafts of light that comes out to kill the undead? I have used this item in other games, and it seems to do diddily.

If all it does is spread disease, seems stupid to use it against the undead and they are already dead and disease isn't going to do squat against them.

Thanks!