The clay documents, when wanted for instruction or as evidence, were carefully baked; and thus it is that they have come down to us, despite their fragility, often in as legible a condition, with the letters as clear and sharp, as any legend on marble, stone, or metal that we possess belonging to Greek or even to Roman times.

The best clay, skilfully baked, is a material quite as enduring as either stone or metal, resisting many influences better than either of those materials.
It may still be asked, did not the Assyrians use other materials also?
Did they not write with ink of some kind on paper, or leather, or parchment?
It is certain that the Egyptians had invented a kind of thick paper many centuries before the Assyrian power arose; and it is further certain that the later Assyrian kings had a good deal of intercourse with Egypt.

Under such circumstances, can we suppose that they did not import paper from that country?
Again, the Persians, we are told, used parchment for their public records.

Are not the Assyrians a much more ingenious people, likely to have done the same, at any rate to some extent?
There is no direct evidence by which these questions can be determinately answered.

No document on any of the materials suggested has been found.