Quote Originally Posted by Redmeth
You don't have to just upgrade them to the next level, if they're already at lvl 5 you might have to tear down but not 100% sure.
This all doesn't sound right... You shouldn't have to tear down anything.

But, to answer the question, all Celtic reforms are shared between the Celtic factions, and so are their conditions. The conditions for the first reforms are the Celts having four large markets in their settlements, combined. The second reform is triggered by six markets, four large cities and six awesome (huge? magnificent? The top-tier temples, nevertheless) temples.