1. The Beastiary is a building where you can use rune shards to unseal monster from seal stone. Carrying the monster in march or battle will greatly improve your power!

 

2. When the Acropolis reach level 10, you need to use the "Unlock Beastiary" item to unlock the Beastiary.
Note: By clicking on the Bestiary building, you can get free fragments to unlock the Bestiary.