Oxford History of India
http://penelope.uchicago.edu/Thayer/E/Gazetteer/Places/Asia/India/_Texts/OXFHOI/1/1*.html
http://penelope.uchicago.edu/Thayer/E/Gazetteer/Places/Asia/India/_Texts/OXFHOI/1/2*.html
http://penelope.uchicago.edu/Thayer/E/Gazetteer/Places/Asia/India/_Texts/OXFHOI/1/3*.html
http://www.historycentral.com/dates/600bc.html
Ashoka's empire
http://www.columbia.edu/itc/mealac/pritchett/00maplinks/early/ashoka/ashoka.html
http://www.ancientindia.co.uk/staff/resources/background/bg1/bg1pdf.pdf
