"In 1933 two sets of gold and silver plates recording in the three forms of cuneiform, Ancient Persian, Elamite, and Babylonian, the boundaries of the Persian Empire were discovered in the foundations of Darius' hall of audience. A number of inscriptions, cut in stone, of Darius I, Xerxes I, and Artaxerxes III indicate to which monarch the various buildings are to be attributed. The oldest of these on the south retaining wall gives Darius' famous prayer for his people: "God protect this country from foe, famine and falsehood."

Interesting so Joseph could have found plates with writing on them.

http://www.sacred-destinations.com/iran/persepolis.htm