OK, according to the only source I have on hand (Akira Nakanishi's "Writing Systems Of The World"), "writing" is accomplished using Alphabets, Syllabaries (where a character has a given sound but contains no inherent, specific meaning), and/or Ideograms ("Any picture, stylized picture, or abstract symbol used in writing a language [emphasis added] and representing a meaning rather than a sound ... [includes] ... Chinese characters, hieroglyphics, and pictograms" (wherein, say, a circle might = the sun).
Any of these are required for writing, so Heavens only knows what the folks in charge of the tech tree were thinking.
dh_epic does raise the contemporary point that simple mathematics and pictograms (i.e., markings to note how many amphorae of wine are in a crate -- notations for inventory, in effect) precede other more advanced systems -- which themselves, by definition, precede Writing as the word is commonly used.
-Oz