Mesopotamia is advanced because they had the first writing system called cuneiform. The first written laws were written in cuneiform. Cuneiform was written by scribes the scribes wrote on clay tablets with a tool called the (stylus).
Mesopotamia Writing systm
Cuneiform comes from a Latin word (cuneus) witch stains for wedge the wedge or stylus was used to wright stories. They used shapes and arrows to tell what they were saying in the writing they or the scribes wrote. The scribes wrote letters or took notes for the king/emperor and it was all written in cuneiform.