Urban buildings constructed in historic city centers of Europe and America in the late 19th and early 20th Century demonstrate a remarkable consistency of architectural excellence and harmony which can be observed from the large urban forms, down to minute details. The comprehensive system of design principles employed by architects of the time in the creation of these buildings has resulted in urban environments that achieve a very high degree of functionality as well as adaptability to the evolving needs of their modern populations. This essay explores the specific physical design techniques employed by architects of the late 19th and early 20th Century to achieve these remarkable results.