How long did Sumerian remain in use as a written language?

Sumerian was first attested around 3100 BCE and remained in use as a written language for approximately three millennia. Although it was replaced as a spoken language by Akkadian around 2000 BCE, it continued to be used in writing until the beginning of the Christian era, marking the end of the use of cuneiform writing.1

During this long period of written usage, Sumerian was maintained through the study of the language in Babylonian schools, where scribes copied literary compositions and created grammatical treatises and dictionaries to preserve the language. Even in the later stages of its history, such as in Hellenistic times, there is evidence of Sumerian words being transcribed in Greek letters.12