Walkthrough tips, Discussion of Campaigns [Heroes 5]

Guys! I'm really puzzled! In the 3rd mission for Necropolis, you need to find 3 artifacts. So, HOW do you turn a Mage's town into a Necropolis?:confused: :confused: :confused: And where, for the love of all that is Necropolis, can you BUILD 20 Bone Dragons?