In the fourth millennium BC, Mesopotamia created a writing system. The writing was created with a triangular stylus, which resulted in the angular form of the strokes. This form of writing is known as "Sumerian cuneiform." Sumerian was used for more than 1000 years before being replaced by Akkadian around 3100 BC. Triangular-shaped symbols were used to write down accounts and business documents using a method called "cuneiform" (wedge shaped). Cuneiform is still used today in some parts of Asia and Africa to mark ownership of property or pay taxes. The first written records we have are dating back to about 4000 B.C. They are notes on clay tablets from ancient Mesopotamia. These notes were used to account for goods being traded or soldiers being hired. They also included recipes for cooking foods such as lamb kidneys wrapped in fat sheep skin. Around 3500 B.C., two different groups in Mesopotamia started using cuneiform independently of each other. One group used it to write down poems and stories while the other group used it to record objects and transactions. Around 3000 B.C., the poets started writing in their own language instead of using Sumerian.