Notre-Dame de Paris, the so famous Catholic cathedral standing on Ile de la Cité in Paris, was built in 1163, largely completed by 1260, then frequently modified in the following centuries until a major restoration between 1844 and 1864. All these steps of construction and modifications involved the frame, so-called “la forêt” (the forest). So, the woods used throughout the cathedral’s history are samples and memories of the forests of oaks grown in the Paris Basin since the Middle Ages. The unfortunate destruction of the cathedral on 15th April of 2019, which miraculously spared a part of the frame, made these woods accessible to the scientific community. Some scientists are particularly interested in the isotopic composition of wood as memory of past climate and as a clock to the past. On one part, the oxygen and carbon isotopes (d13C and d18O) of tree-ring cellulose will bring light to past climate. Indeed, the isotopic composition of this component is determined by the conditions surrounding the trees during their growth. The variations of d13C and d18O with time, recorded in the successive rings built by the trees year after year, allows reconstructing the evolution of some
environmental or climatic parameters such as temperature or humidity. Isotope dendroclimatology, a
rapidly expanding field of investigation, is applied to old living trees, sub-fossil woods from buildings or even fossil material to reconstruct past climate. This methodological approach will be applied to the cathedral's oak timbers that have escaped severe charring and to contemporaneous unburned woods from other buildings (Figure 1). On the other part, measuring ring by ring the residual content of 14C isotope in cellulose will make it possible to refine the 14C clock which allows to date any material containing carbon. This will be achieved by providing new portions of the global calibration curve for the continental Western Europe from the 12th to the 18th century, from uncharred "forest" of Notre-Dame.

Daux V., Hatté C., duBoisgueheneuc D., Beck L., Richardin P. The ‘forest’ of Notre dame de Paris: a path into medieval climate and time. Journal of Cultural Heritage, In press