Notations on tokens and envelopes. Some of the envelopes have markings corresponding to the clay shapes inside. Moreover, these markings are more or less similar to the shapes drawn on clay tablets that date back to about 3100 BC and that are unambiguously related to the Sumerian language. These markings are thought to constitute a logographic form of writing consisting of some 1,200 different characters representing numerals, names, and such material objects as cloth and cow.