Invisible Wall

Our Fortecia is a bur in the throat for the nearby creatures. A large number of ghostly and distorted creatures pass through the area. If they attack all at once, we are finished.
To prevent this from happening, we have special contraptions on the walls that need to be charged with Spark energy. {username}, I ask you to check them. If they are out of juice, recharge them.

If the generators don't work, all the hostile creatures that live to the west of the city will be drawn here.

Excellent! Thank you for your service. We can hold out for a while, and then – I hope – reinforcements will arrive...