"My hope is to dispel the idea, so widely and uncritically held, that cities are a kind of grand accident, beyond the control of the human will, and that they respond only to some immutable law. I contend that human will can be exercised effectively on our cities now, so that the form that they take will be a true expression of the highest aspirations of our civilization. Edmund N. Bacon Design of Cities The growth of cities is often described as continual metamorphoses. On the one hand, it may be viewed as organic, as though a city is a biological entity following "immutable laws" of nature - evolution and natural selection, perhaps. On the other hand, Edmund Bacon's work and writings testify to human intervention as the controlling influence in this process. The planned evolution of a city can (must) be viewed as an inevitable consequence of a design idea. This paper will explore the metamorphosis of Philadelphia, past and anticipated, as a human construct - a social environment. Philadelphia is the United States' most successfully planned city and Edmund N. Bacon is its most notable planner. In his era of influence and power, Bacon harnessed multi-discipline teams of professionals - architects, politicians, sociologists, landscape designers. Their integrated efforts under his leadership are a legacy of urban achievements from macro-scale (Penn Center) to micro (Society Hill).As the 1991-92 recipient of the Plym Distinguished Professorship at the School of Architecture, University of Illinois at Urbana-Champaign, Bacon collaborated with a design team led by the authors and colleagues to critically address his work of the past 40 years and to create a vision for Philadelphia for the next 40. Bacon's charge: "Prepare drawings and models of the entire two mile extent of the Center City west bank of the Schuylkill.. . which stretches into the 21 st Century concepts, showing the opportunity to build a splendid city like none that has ever been built before."This paper will discuss the results of this collaboration among students and Edmund Bacon and it will consider its implications for succeeding metamorphoses of city environments in which groups and individuals can live, work, and play."