The history of ancient India has been reconstructed with the help of a wide variety of historical sources and tools. Unlike modern historians, who have access to systematic records, census reports, newspapers and official documents, historians of ancient India have to depend mainly on archaeological remains, inscriptions, coins, literary works, foreign accounts and material evidence. These sources are particularly important for understanding the evolution of social structures in India, including the development of family, kinship, caste, class, tribal communities, occupations, gender relations and institutions. Archaeology is one of the most important tools for writing the history of ancient India. Excavations of settlements, cities, burial sites, monuments, pottery, tools, weapons, ornaments, houses and agricultural remains provide information about the material life of ancient people. The remains of the Harappan civilisation, for example, reveal the existence of planned cities, differentiated residential areas, craft production, trade networks and social differences. Sites such as Harappa, Mohenjo-daro, Dholavira and Lothal help historians understand the organisation of early urban society. Archaeological evidence from later periods also helps in tracing changes from tribal and rural communities to settled agricultural and urban societies. Inscriptions constitute another major historical tool. Ancient rulers, religious institutions and individuals recorded information on rocks, pillars, copper plates and temple walls. The inscriptions of Ashoka are particularly valuable because they provide direct evidence about his administration, religious policies, moral principles and relationship with different sections of society. Later inscriptions provide information about land grants, taxation, occupations, social groups, religious institutions and political authority.