National Geographic  The people known as Sumerians are credited with starting the first civilization and building the first settlements worthy of being called cities. They also invented writing, and then they wrote and wrote and wrote, filling millions of tablets with their intricate, detailed characters.

They left behind everything from religious texts to poetry to receipts, much of which remains preserved 5,000 years later. Understanding the symbols they etched in clay is another matter. The oldest known language left no descendants.