The essence of transformations is the essence of architecture itself: to build upon what's already there, not only metaphorically but also literally. This principle has a very long history, in Europe going back to at least the reuse of Roman building parts (spolia). Sometimes it even led to the transformation of complete buildings, such as the Diocletian Palace which over time has become the city of Split. Only in the modern (and postmodern) era of obsolescence, the habit of reuse lost traction, and some of its attraction. Building upon history became almost principally incompatible with the modern ideal of breaking with the past. Yet the idea of reuse and repurposing never completely disappeared in the twentieth century and it had already begun to make a comeback in the first postwar decades, which were in many ways the period of peak modernity, and peak obsolescence.
In the modern understanding of the past there was an allocated place for historical architecture. at least, for those projects which were perceived as untouchable monuments, and which were quarantined in splendid isolation. In buildings of uncontested historic value nothing could be added or taken away; all other buildings were simply considered old, and could indiscriminately be demolished, improved or modernized.
Excerpt from: Hans Ibelings and diederendirrix architects, Make it Anew (Amsterdam/Montreal: Architecture Observer, 2018)