“Around 2800 B.C. scribes turned the pictographs on their sides and began to write in horizontal rows, from left to right and top to bottom. . . . About three hundred years later, writing speed was increased by replacing the sharp-pointed stylus with a triangular-tipped one. This stylus was pushed into the clay instead of being dragged through it. . . . This innovation radically altered the nature of the writing; pictographs evolved into an abstract sign writing called cuneiform (from the Latin for “wedge-shaped”). . . .
As early scribes developed their written language to function in the same way as their speech, the need to represent spoken sounds not easily depicted arose. Adverbs, prepositions, and personal names often could not be adapted to pictographic representation. Picture symbols began to represent the sounds of the objects depicted instead of the objects themselves. Cuneiform became rebus writing, which is pictures and/or pictographs representing words and syllables with the same or similar sound as the object depicted. Pictures were used as phonograms, or graphic symbols for sounds. The highest development of cuneiform was its use of abstract signs to represent syllables, which are sounds made by combining more elementary sounds.”

—Phil Meggs & Alston Purvis, Meggs’ History of Graphic Design, 2006.