Oldest Written Document That's Ever Been Found

It's a clay fragment.

From the piece on Physorg.com...

A tiny clay fragment - dating from the 14th century B.C.E. - that was found in excavations outside Jerusalem's Old City walls contains the oldest written document ever found in Jerusalem, say researchers at the Hebrew University of Jerusalem. The find, believed to be part of a tablet from a royal archives, further testifies to the importance of Jerusalem as a major city in the Late Bronze Age, long before its conquest by King David, they say.