I am sorry to inform you that the game softlocked in the second area for me with no clear cause; I have 50 Denarii and neither Knight nor Barbarian cost that much, but I can't place either for some reason? I just get their transparent sprite in the center, depending on whether I clicked their buy-tile most recently. Can't even make a barricade.
Edit: I'm on browser, and reloading seems to fix it, but it came back again with the next area. I did buy new characters each time?
Further edit: losing and restarting the arena gives the same glitch. Losing and going to the main menu before restarting the arena... still gives me the same glitch.