Suburbanization has led to the agglomeration of employment and business activity at subcenters removed from the Central Business District (CBD). To address the development of these subcenters in the past half century, this study revises the Standard Urban Model by: 1. Tracing historical origins and variations of the model over the many millennia; 2. Developing a negative-exponential model of agglomerative employment and business subcentering based on the historical findings; and 3. Testing this model using a comparative t-test and a Davidson-MacKinnon model-specification error test to ascertain the existence and location of peak subcenter activity. On average, the distances of the employment and sales peaks occur midway between the CBD and the furthest Major Retail Centers. This volume explores the development of the monocentric urban model. Throughout the following chapters, the history of the concept, the development of the general model, and the creation of a specific model, which includes subcenters, are considered. Next, the specific model is tested against business-census data for ten radial monocentric cities in the United States. Results and implications are reported. Finally, a survey of research that grew out of the initial research and that has extended from the date of the initial project through the present time is presented. Chapters 1 through 5 contain the development of the spine of the research. Chapter 6 contains a brief of major research elements built upon the spine. There has been an increase in agglomerative subcentering over the past four decades in many large metropolitan areas. What present society describes as urban sprawl or suburban flight may simply be a natural process of urban-regional development, consistent with monocentric urban thought and development extending backwards in time for more than two millennia. By objective, the theoretical work of this book emulates major monocentric models developed over the past three millennia to develop an extended mathematical model with agglomerative subcenters. Next, the empirical work tests this extended model against observations of Major Retail Centers (MRCs) for radially monocentric SMSAs. Through a two-step econometric technique which includes a model-specification error test, the results ascertain the existence and locations of peak subcenter activity at an average of approximately half the distance from the Central Business District to the furthest MRC. This position concurs with Plato's ideal model of Magnesia and other works of the past three millennia. Fundamentally, the inspiration and intuition for this book comes from a lifetime of oral and written cultural tradition. Building upon this tradition, this work uses the historical chronicles and analyses found in Chapter 2 to develop the theoretical model in Chapter 3. In retrospect, the empirical Results, in Chapter 4, support the theory of peak subcenter activity developed in Chapter 3.