These developments provided the basis for densely populated settlements, specialization and division of labour, trading economies, the development of non-portable art and architecture, centralized administrations and political structures, hierarchical ideologies, depersonalized systems of knowledge (e.g., writing), and property ownership[citation needed]. Personal land and private property ownership led to hierarchical society, class struggle and armies[citation needed]. The first fully developed manifestation of the entire Neolithic complex is seen in the Middle Eastern Sumerian cities (c. 5,500 BP), whose emergence also heralded the beginning of the Bronze Age.