This work presents the results of the characterisation of the mortars used to build the vaults of the choir and a transverse arch in the nave of Notre-Dame de Paris. The aim is to highlight the mixes used and technological choices made by the builders at the end of the 12th century. A multi-analytical approach made it possible to characterise the binders, aggregates, particle size distributions and the physical and chemical properties of about thirty samples. They lead to the definition of mortar mix equivalent to medieval ones. First investigations conducted on the fresh mortar show its ability to erect an arch or the panels of the vaults and validate the mortar mix proportions. These results will sufficiently support the ongoing project on the reconstitution of compatible mortars as well as on modelling the structural comportment of the edifice.