In Aternum several Bosses are wreaking havoc. They have their own camp in which they are planning their next steps. Lay siege to their camps and defeat them multiple times to get rid of them!
Boss battles are more difficult than ordinary PvE battles in the same area of the map. If you win a battle against a Boss, you also get better rewards like rare or better Forge Materials, Shards, and more Gold.
After defeating a boss, you have to wait a certain amount of time before you can attack again.
You can defeat a Boss up to 30 times, before he will retreat and never come back.