Spolia (from the Latin ‘spoils’) is the name given by architectural historians to (typically stone) fragments of earlier buildings that have been repurposed to serve as part of later buildings.

In the west, spolia are probably most closely associated with the period spanning the late Roman empire and the early middle ages- a period of decline in resource availability and technical ability, in which scavenging older or derelict buildings for building materials was common.

The practice is a good illustration of the writer John Michael Greer’s theory of ‘catabolic collapse,’ which uses the analogy of biological metabolism to explain the life-cycles of human civilisations. When civilisations are on the rise, they grow in an ‘anabolic’ manner, whereby ‘cheap and easy’ energy is consumed to combine simple elements into more and more complex structures, just as the human body transforms dietary proteins and energy into muscle. When energy is no longer cheaply or easily available, civilisations enter their decline and collapse phase, and their complex structures are broken down via ‘catabolic’ processes into simpler elements in order to unlock the energy and resources they contain, just as a starving organism will cannibalise its own muscle to meet its energy requirements. Think of the energy inputs, technical expertise and apparatus needed to produce and distribute even something so seemingly simple as dimension lumber, and then to assemble it into the form of a house; compare this with the act of pulling the house down and burning its timber to stay warm.