Banner

The banner is the lifeblood of your colony. Using the Banner Tool (the key on the hotbar), you can place your banner anywhere in the world large enough for it to fit.

While in the Banner Tool, you will see a green area and a red area. Zombies will not spawn inside the green area, but will spawn in the red area in relative proximity to your banner. This safe area is a cube, centered on the banner and with a radius of 30 blocks, which can be increased to a maximum of 100 with Science.

After placing the banner, you may right click on the banner or the banner tool to open an interface with two options, "Science" (which can also be accessed via the key) and "Recruit a colonist." Recruiting your first colonist costs 8000 food, and by default they will consume 2000 food each day after. Colonists will spawn directly on top of your banner.

If the player dies, they will respawn at the banner. If a zombie reaches the banner, random colonists will begin to take damage. Zombies will continue to attack the banner until all colonists are dead if you do not kill them.

Siege Mode
The banner must be accessible from the outside. This means there must be a clear path from your banners location to the red area outside of your base. The most common strategy for remaining safe while unable to close off your colony is to create a winding path which zombies must follow to reach your banner (if there is only one path to your banner, zombies will follow it and you will be able to station guards along its length). If you do close off the area to the outside, your colony enter siege mode. In siege mode, your colonists will consume 6 times more food each day. Currently, siege mode only activates in the spawning phase of zombies, and will deactivate during the day or late night.

Banner Removal
Colonists require a banner to function. Attempting to remove the banner will trigger a warning reading "removal of this block may cause problems in your colony." As long as it is short-term, this will not break your game. Moving the banner is perfectly acceptable, however unemployed colonists will stand around the spot where the banner used to be with a "no path" error icon over their head. You will also enter siege mode, which will stop once your banner is replaced.

Troubleshooting
One of the most common problems with mazes is siege mode triggering despite a clear path through a long path. Currently the zombie AI will only path a few hundred blocks. If your path is more than a few hundred blocks, zombies will not be able to path down it and siege mode will activate. The fix for this issue is shortening the path by 20-30 blocks in length each night until siege mode does not activate at night.