In the current context of worsening climate change, depletion of natural resources and environmental damage, the concepts of recycling and, more broadly, the circular economy, have developed over the last few years. These concepts, cloaked in contemporary rhetoric, take up a principle - re-use - that is as old as human societies, but which was lost with the Industrial Revolution and, above all, the development of the so-called consumer society in the second half of the 20th century.

The construction industry has not escaped these changes. During the twentieth century, in the most industrialised countries, architecture gradually came to rely essentially on new, standardised materials produced on an industrial scale, relegating the use of second-hand materials in construction to a marginal role. This makes it all the more important to look back over a long period of history - from recent prehistory to the twentieth century - to analyse the recurring phenomenon of reuse in construction.

The international colloquium ‘Remploi: matérialité et symbolisme, de la Préhistoire au XXe siècle’ (Reuse: materiality and symbolism, from prehistory to the 20th century), to be held in Nantes on 27, 28 and 29 November 2025, will highlight the role played by reused materials (stone, wood, earth, metal, glass, etc.) in architectural production in ancient societies. This will be understood in the broadest sense of the term: from ‘minor’ buildings to the largest monumental complexes, including the various forms of housing. The chronological perspective will be that of the long term, from recent prehistory to the 20th century, and the main area of study will be Europe.

By drawing on the approaches of archaeologists, architectural historians and textual historians, or a combination of these, the aim will be to examine the extent and methods of this phenomenon. While the definition of this re-use does not seem to pose any difficulty (use of elements and materials from a previous construction), the challenge will be to develop a discourse that is accessible to academic traditions that are sometimes very different.

We will be focusing on a number of different aspects of the reasons for this use, some of which are polymorphous. This re-use can be considered in its strict materiality, in its technical and architectural dimensions: fixed polishers included in the walls of Anjou dolmens, orthostats from a single fractured slab at the Barnenez cairn (Finistère), or grooved slabs used to form the walls of certain Angoulême dolmens, visigothic materials in Umayyad buildings on the Iberian Peninsula, ancient capitals in Santa Maria del Trastevere (Rome) or ancient bas-reliefs in the caliphal palace of Madinat al-Zahra (Cordoba), etc. What materials are used? Are they re-cut and modified? Where are they placed in the new construction? When materials are commonly reused in construction, as was the case, for example, in elite buildings in the Middle Ages or in peasant housing until the beginning of the 20th century, how is the material reused

Reuse can also be used for economic reasons: the reuse of materials during the reconstruction of Orléans Cathedral after the Wars of Religion, and the plundering of marble from the Colosseum from the Middle Ages to the 16th century. For older periods, with a smaller body of documentation, the question needs to be asked: was the construction of Calatayud (Aragon) using materials from the Celtiberian and Roman town of Bilbilis from the 9th century onwards purely for economic reasons? Lastly, reuse can be motivated by symbolic, ideological or even political reasons, some of which are clearly demonstrated by research: the reuse of materials in the Umayyad mosque in Cordoba, interpreted as a means of legitimising the dynasty; the inlaying of ancient bas-reliefs on the façade of the Villa Borghese in Rome, symbols of the power of this papal family. Does the logic behind the use of inlaid bas-reliefs vary according to the nature of the building: religious, civil, military, etc.?

In the case of megaliths, the opportunistic nature of such action can be questioned when these materials carry symbolic representations that are mobilised for the construction of a new edifice. Was it the material envelope of these blocks of stone that was mobilised, or rather the human and non-human beings attached to them?

As we can see, the approaches proposed are multiple: during the colloquium, the perspectives and examples from different periods called upon by the various papers will be presented in a cross-disciplinary manner, so as to mutually enrich each other and arrive at a discourse common to all our academic practices.