I thought it was one of KaHmnd's stories but I can't find it here, xnxx, or the Wayback machine.
A very powerful mage is traveling, I think with gypsies, in a wagon/caravan. The section that I am looking for is that he uses a piece of an ancient library to create an illusion of the library just before it burned. He then takes the books through the illusion just before the fire.
An other mage from the Council(?) with him almost soiled his robes because the fire could have come through as well.
The mage creates a new wagon to hold the library and later gets someone else to care for it.
the other details might be from other stories:
he was an Archmage
The council did not trust him
He did not care about the council's edicts
He made the wagons by transforming wood