ABSTRACT
Introduction The 20lh cenlul}' wUl be remembered for many lhings - devastating wars, remarkabJ technological change, the human JKIpulation explosion, environmental degradation - bul p rhaps above all for the dramalic urbanizat.ion of human societies. Al the beginning of the present cenlul}' about 150 million people lived in cities and lowns -less than one In I n of what was th n the world's JKIpulation; by the end of this centul}' this figure wiu have increased twenty-fold amounting 10 half the world's population. In 1900, only five or six urban regions had more than a miUion people. By 2010 a similar number win each have a population of mo Ihan 20 million. In the unfolding of human experience the 20!.h cenlul}' will have been!.h bridge between !.he lasl rural century and the first urban cenllll}'.
