[Tollund]

It's definitely very effective. I have a compstomp game with a friend going where I have both the Summoning Circle (60% blood spell reduction) and the leper fens (Spreads deadly disease, 1D1W) in the same province. This would be a difficult/expensive thing to work around except that I'm playing Midgard so all of my Galdermen regenerate. After ~20 turns of being diseased, most only have one or two extra afflictions.