Darion is the place where you start from - King Mark's castle. When you finish your work in Teana, you're ported back there and offered a multitude of free troops - paladins, knights, horsemen, archmagi, inquisitors, priests and archers (and I suppose Rune Magi in KBCW) to use in your battle with the archdemon Baal.
This is also a tip - if you want to use some non-human troops in the final battle, stock up on them in advance before going back to Darion.
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