Why did the Magic Council make so many Faces? If Face can eradicate all magic on Fiore, why did the council make so many of them?

Magic is their first line of defence, after all, they are the Magic Council. But even if something did come up where they needed to eradicate magic, why would they make so many Faces, especially if they were trying to keep them a big secret? 

I could understand if there are 2 or 3, but why hundreds?

If they had multiple, it would make more sense to spread them out, but why would they keep them all in the same place?
My guess is because of people like Zeref.

It's the last line of defense. If all else fails, they had enough Faces to make sure the eradication of magic would be complete. Of course, that plan failed too.

That would be my thought process: if magic couldn't stop magic, eradicate it.