Hills Siege

Periodically, NPC towns will come under siege by the Obsidian Cabalists. The timing, duration, and location of these sieges are driven by Celestial Mechanics. When you attempt to enter a town under siege, you have the option to enter the Town Siege scene where the enemy has made camp outside the town and is fighting the town defenders. You can choose to join the battle and end the siege early or work your way around the perimeter, perhaps encountering only some scouting parties.

NPCs

 * Scout

Bosses
These Boss creatures will spawn once all 18 Siege Engineers have been eliminated from the Siege.

For a prediction on where the Cabalists will spawn : Moongate Travelers Siege Mapper!

Trivia

 * Catapults in Sieges are now attended by a team of Tier 8 engineers and guards who defend and operate the catapult. Only when three waves of engineers are killed will the catapult cease firing. Additionally, killing those engineers has a chance to yield a recipe for a tabletop catapult decoration and lots of lumber as loot. Note that killing the engineers is now what triggers the appearance of the liches, not destroying the catapults.
 * Town Sieges Voluntary Entry: Town Sieges can now be bypassed by all level of players, allowing direct access to the besieged town. This is part of an overall effort to reduce the number of scene loads in each play session. Sieges can now be entered voluntarily from the Overworld, just like any other adventure scene. Note when leaving towns you automatically bypass sieges (no option is given to enter them).