Priest levels on the unit you want to build the temple.
On that note, I'm perplexed how Blood Dominion is supposed to work. Clearly, their Dominion is stronger than mine because on either side of a continental mountain range, where dominion can't spread through, my Dominion reigns. But even across an ocean of provinces I own, enemy dominion is completely flooding me. I have B3 guys with Jade Knives working over time, and for the most part they barely make a dent within half a continent of a homeland.
I started with Dominion Strength 8, so I know it's a little weak but I thought extra temples were supposed to take it to 10. I've got three guys sacrificing in a circle around an enemy homeland, and have watched dominion go up, down, left and right. I know it's a temple check and it's random, but why does Dominion not spread from behind where the enemy dominion can't reach? Another nation doesn't have temples within 10 provinces of my sacrificiers, and they're dominion is still smoking mine.
Is Mictlan just, fundamental weaker when it comes to dominion spread? Because playing just about any other nation, even at the same comprable dominion strength, I've never been this far behind. I suppose I'm probably just not doing it as I'm supposed to, and having a temple and sacrificer in literally every other province.