While the Crystarium is self-sufficient to a degree, we still need people to travel farther afield to get what we can't produce ourselves. That's where leves come in handy.
In times of conflict, a steady flow of supplies is just as important as strong defenses and whatnot.
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With the sin eaters no longer the threat they once were, we can concentrate our efforts on providing a wider variety of goods for the people of the Crystarium.
Compared to the Warriors of Light who are out there fighting, we artisans may not garner much attention, but we have a vital role to play nonetheless. And play it we will, for the future of our city.