I have played a test game for the barb conquest challenge, up to about 500 BC. The good news:
All civs have two cities but no improvements left. I am able to kill all settlers that they try to send out using my Keshiks. Naturally, their research rate is now disastrous.
I have gifted Iron Working to all of them, so the barbs should soon be able to spawn swords. Meanwhile I am beelining Construction for some cats for culture defense removal.
And the bad news:
I have yet to see a barb axe spawn, and only very few archers have spawned so far.
The only city the barbs have managed to capture is one of mine that I deserted for them. But even if it contained the Stonehenge they have still not gained a culture expansion despite sitting on the city for 15 turns. Bug? Or can barb cities not gain culture?
This is going to be a tricky one.