History of the world
Whether in prehistoric or historic times, people always needed to be near reliable sources of potable water. Settlements developed on river banks as early as 3000 BCE in Mesopotamia, on the banks of Egypt's Nile River, in the Indus River valley, and along China's rivers. As farming developed, grain agriculture became more sophisticated and prompted a division of labour to store food between growing seasons. Labour divisions led to the rise of a leisured upper class and the development of cities, which provided the foundation for civilization. The growing complexity of human societies necessitated systems of accounting and writing.
History of Bulgaria
The eneolithic Varna culture (5000 BC) represents the first civilization with a sophisticated social hierarchy in Europe. The centerpiece of this culture is the Varna Necropolis, discovered in the early 1970s. It serves as a tool in understanding how the earliest European societies functioned, principally through well-preserved ritual burials, pottery, and golden jewelry. The golden rings, bracelets and ceremonial weapons discovered in one of the graves were created between 4,600 and 4200 BC, which makes them the oldest gold artifacts yet discovered anywhere in the world. The Karanovo culture developed simultaneously with the one in Varna, and its earth layers serve as a stratigraphical gauge for the prehistory of the wider Balkans region.