Also known as "Copper Age", the European Chalcolithic was a time of changes and confusion. The most relevant fact was the infiltration and the invasion of large parts of the territory by people originating from Central Asia, which is considered by mainstream scholars to be the original Indo-Europeans, but there are again several theories in dispute. Other phenomena are the expansion of Megalithism, the appearance of the first significant economic stratification and the related first known monarchies in the Balkan region.