First writing may have been three-dimensional
Archeologists have long been puzzled by large numbers of small, fired-clay objects found in the Middle East. Denise Schmandt-Besserat, University of Texas at Austin, believes that these small geometrical shapes (cones, spheres, disks, etc.) were actually symbols used in commerce to indicate numbers and types of commodities (sheep, oil, etc.). Generally less than an inch in size, the clay objects were apparently sealed in hollow clay spheres to make bills of lading as early as 8,500 B.C. This is 5,000 years before two-dimensional clay tablets were introduced for writing.
(Anonymous; "From Reckoning to Writing," Scientific American, p. 58, August 1977.)
Comment. These clay symbols might be related to the painted pebbles and small carved stone balls found in Europe.