Siege mode

Siege mode activates for a colony when Zombies do not have a valid path from the outside to the Banner. I.e. when the colony is fully enclosed within walls or a mound that zombies cannot cross. To avoid siege mode there has to be at least one entrance through which zombies can walk. The player should place Guards to protect that entrance.

For a normal colony each Colonist requires one meal per day to survive. During siege mode food consumption increases dramatically which can bring the colony to starvation very fast.

Mazes
Players sometimes build mazes in front of the entrance to increase the walking time for zombies and keep them within range for guards for a longer time. With very long mazes it can sometimes happen that siege mode does activate on its own and / or randomly. This means that the walking path trough the maze is too long for the game's AI and it is recommended to reduce the total path length.