Сайт за българска история и електронна библиотека
University of Pennsylvania press. Philadelphia. 2012. History of civilizations of Central Asia: Volume I. The dawn of civilization: earliest times to 700 B.C. Volume II. The development of sedentary and nomadic civilizations: 700 B.C. to A.D. 250. Volume III. The crossroads of civilizations: А.D. 250 to 750.