As in the title, if the AI has a town at 8 tiles from the spot (statue) in the ruins of Imperium, like in my current game, it's impossible to build a town here and finish the quest.
By the way, Fallen Enchantress is, in its beta state, already great. The final result will be fantastic ! Thanks Frogboy and Stardock for not letting, after WoM, the idea of Elemental fade away !