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So, can you choose to build either one or the other building?
Or is it an upgrade?
Each faction has 4 unique buildings, and you can build 2 of them.
For the Knights, it's 10% to the speed of accumulating racial resources or illuminating an area once a week.
And also resurrection, or I forgot what, but it's also a good bonus.

Барон "Vampires"
Отдай свои прошлые сны,
В сомненьях себя обрети,
В бешеном танце душа кружится!
Не думай, что будет потом,
Здесь и сейчас мы живем,
Стань хоть на миг сам собой, слышишь!