They only have one monopoly: Fine Pottery
We're a couple of centuries behind them, our last Pottery improvement was Ash Glazing...from a Xohyssiri refugee.
The Xohyssiri also have extremely cheap Grand Sacrifice due to Moloch Calls. A Grand Sacrifice of 300 children is massive and everyone will be sure the spirits are placated...but 300 kids won't even be a visible blip on their population cost.
They're functionally running an Econ 0 Secondary Grand Sacrifice.
But I don't really see the point, given their traits, the moment the Thunder Horse OR the Highlanders gain dominance, they're going to crush the Xohyssiri because their traits are offensive to every single neighbor.
And if the Thunder Horse lose enough Prestige beating on the Highlanders, the Xohyssiri are going to break away.
You can see their strategy actually if you think about it:
-Discover Center of Trade through dominance of Pottery. Obtain +1 Diplomacy per turn.
-Trigger Golden Age through overflowing Diplomacy and Art
-Obtain Step Farms from Ymaryn to improve their Expand Economy rate.
-Pump overflow and keep churning the Econ slots they have frantically into even more Art Patronage to overflow even more.
-Once Mysticism overflow starts pouring into Economy, crank it all into Expand Army. Trigger Martial overflow deliberately once all stats are maxed.
-FREEDOM
Not strictly true. Water going into a city still comes out, if not directly usable by people, it's perfectly usable(and in fact superior due to the nutrient rich iron age sewage water) by bocages.
Which would buy a few Forest expansion slots I think? Aqueducts do generate 4
