The most important archaeological discoveries in Sumer are a large number of tablets written in Cuneiform. Sumerian writing is the oldest example of writing on earth. Although pictures - that is, hieroglyphs were first used, symbols were later made to represent syllables. Triangular or wedge-shaped reeds were used to write on moist clay. This is called cuneiform. A large body of hundreds of thousands of texts in the Sumerian language have survived, such as personal or business letters, receipts, lexical lists, laws, hymns, prayers, stories, daily records, and even libraries full of clay tablets. Monumental inscriptions and texts on different objects like statues or bricks are also very common. Many texts survive in multiple copies because they were repeatedly transcribed by scribes-in-training. Sumerian continued to be the language of religion and law in Mesopotamia long after Semitic speakers had become
the ruling race. The Sumerian language is generally regarded as a language isolate in linguistics because it belongs to no known language family; Akkadian, by contrast belongs to the Semitic branch of the Afro-Asiatic languages. There have been many failed attempts to connect Sumerian to other language groups. It is an agglutinative language; in other words, morphemes ("units of meaning") are added together to create words, unlike analytic languages where morphemes are purely added together to create sentences.
Understanding Sumerian texts today can be problematic even for experts. Most difficult are the earliest texts, which in many cases do not give the full grammatical structure of the language.
During the third millennium BC, they developed a very intimate cultural symbiosis between the Sumerians and the Akkadians, which included widespread bilingualism. The influence of Sumerian on Akkadian (and vice versa) is evident in all areas, from lexical borrowing on a massive scale, to syntactic, morphological, and phonological convergence. This has prompted scholars to refer to Sumerian and Akkadian in the third millennium as a sprachbund.
Akkadian gradually replaced Sumerian as a spoken language somewhere around the turn of the 3rd and the 2nd millennium BC (the exact dating being a matter of debate), but Sumerian continued to be used as a sacred, ceremonial, literary and scientific language in Babylonia and Assyria until the 1st century CE.