The cuneiform writing system was in use over more than 30 centuries, through several stages of evolution, from the 30th century BC down to the lst century AD. It was completely replaced by alphabetic writing in the course of the Roman era and has left behind no descendant systems in continued use. For this reason, it had to be deciphered from scratch in 19th century Assyriology. Successful completion of decipherment is dated t0 1857.

The system consists of a comhination of logophonetic, consonantal alphabetic and syllabic signs.

The cuneiform script underwent considerable changes over a period of more than two millennia. The image below shows the development of the sign SAG "head" (Borger nr. 184, U+12295 ) .

Stage l shows the pictogram as it was drawn around 3000 BC. Stage 2 shows the rotated pictogram as written around 2800 BC. Stage 3 shows the abstracted glyph in archaic monumental inscriptions, from ca. 2600 BC, and stage 4 is the sign as written in clay, contemporary to stage 3. Stage 5 represents the late 3rd millennium, and stage 6 represents Old Assyrian ductus of the early 2nd millennium, as adopted into Hittite. Stage 7 is the simplified sign as written by Assyrian scribes in the early lst millennium, and until the script's extinction.

The cuneiform script proper emerges out of pictographic proto-writing in the later 4th millennium. Mesopotamia's "proto-literate" period spans the 35th to 32nd centuries. The first documents unequivocally written in the Sumerian language date to the 31st century, found at Jemdet Nasr.

The Sumerians of the Uruk period used clay tokens to count their agricultural and manufactured foods. They would place the tokens in hollow clay containers and mark the lids with the number of tokens inside. They impressed a picture of the token inside as many times as the amount of tokens. Later they realized that they would not have to use the tokens and the scripture on the containers and started using only the scripture. So they would not have to write 100 pictures for 100 tokens they started making symbols for an amount of tokens. Thus writing began.

Originally, pictograms were drawn on clay tablets in vertical columns with a pen made from a sharpened reed stylus, or incised in stone. This early style lacked the characteristic wedge-shape of the strokes.

Certain signs to indicate names of gods, countries, cities, vessels, birds, trees, etc. , are known as determinants, and were the Sumerian signs of the terms in question, added as a guide for the reader. Proper names continued to be usually written in purely "ideographic" fashion.

From about 2900 BC, many pictographs began to lose their original function, and a given sign could have vanous meanings depending on context. The sign inventory was reduced from some l,500 signs to some 600 signs, and writing became increasingly phonological. Determinative signs were re-introduced to avoid ambiguity. This process is chronologically parallel to, and possibly not independent of, the development of Egyptian hieroglyphic orthography.

詞匯預測：

alphabetic　adj.照字母次序的，字母的
descendant n.子孫，后代
deciphered n，譯解
cuneiform　　adj.楔形的，楔形文字的
pictogram　n.象形圖
orthography　n.正確拼字，拼字，正字法
millennium n.復數(shù)