Asia
The coastal periphery was home to some of the world's earliest known civilizations, each of them developing around fertile river valleys. The civilizations in Mesopotamia, the Indus Valley and the Yellow River shared many similarities. These civilizations may well have exchanged technologies and ideas such as mathematics and the wheel. Other innovations, such as writing, seem to have been developed individually in each area. Cities, states and empires developed in these lowlands.
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.