Why did they store salt in the Palazzo Pubblico in Siena?

I still don’t know the answer to this question, but here are some hypotheses:

-day-to-day government activities involved the use of large amounts of salt
-why get a warehouse when you already have a Palazzo?
-they planned to move it but got lazy
-conveniently close to Palazzo Snack Bar
-to get to the other side
-forty-two