Rodrigo Perez de Arce's essay Urban Transformations and Architectural Additions was published during the formative stages of Post Modernism, at the point where theory was becoming seriously established. Jencks' first essays formalising the term Post Modernism in architecture and the revised Learning from Las Vegas were published the previous year. In planning terms, modernism had become associated with comprehensive redevelopment and forms of urban organisation that ignored context, history and any sense of tradition. De Arce considered the essential nature of buildings and the richness of historic urban form and explored how robust that essence was over time. He looked at the value of essential remnants and rich complexities in maintaining a sense of continuity and relevance. Having explored the adaptation process in history, de Arce went on to see how such a process might be simulated in contemporary cities with modern buildings, using additions and layers to change them from objects in infinite windswept space to being part of a rich urban fabric which described urban place. To do this he used concrete examples; housing schemes by James Stirling, new government centres in Chandigrah and Dacca and more prosaic 60's housing blocks. The paper had a fundamental influence on the way that architects and planners thought about the nature of cities: as dynamic organisms that were tangible to human beings, completely opposite to the systems thinking of the time. It contributed to ideas about the importance of street, place and city block which influenced so much recent regeneration practice. As we enter a phase of development where the reuse and adaptation of existing buildings is becoming paramount from both an economic and sustainable point of view, Perez de Arce's paper gives important insights into how to think about the process positively.