Talk:Castle Expansions/@comment-11612571-20130715145409/@comment-4199297-20130715154148

"3 or 4" is what I've seen mentioned. And from what I've read:

4th forge level1: 20 gems

5th forge level1: 40 gems

6th forge level1: 80 gems

So having more than 3 forges is a decent gem investment. (I'll stick to my 3 level 2 forges, thank you very much...)