Pont de la Margineda (Margineda Bridge) is a Romanic bridge located along the ancient Royal Road that connects St. Julià de Lòira and Andorra la Vella. It is one of the biggest and most slender Medieval Bridges still standing in the Andorra Principality. In ancient times, it was used to cross the river Valira. Margineda Bridge measures approximately 50 meters, and has a semicircular arch. The technical quality of the construction (rubble masonry with mortar joints) is evident from the bridge’s good state of conservation and its high level of integrity throughout its lifespan; it has not experienced any major transformations. The government of the Principality is promoting a comprehensive study of the bridge from a historical, archaeological, and technical-construction standpoint in order to design a restoration project. As part of the project’s multidisciplinary group, the Materials Lab at the Universitat Politècnica de Catalunya (UPC) had the objective of establishing intervention criteria that would design a plan for the interventions to be implemented. The Lab has performed a study of the materials and damage to the bridge, following an analysis methodology and the subsequent assessment of the data obtained as a result. To study the materials, the lab has performed petrologic characterizations of the travertine voussoirs on the edges and the rest of the stones in the masonry, mortar characterizations for identifying their composition, wall readings for determining the bridge’s different construction stages and later interventions. Analyses of patina samples have also been performed in order to establish, on one hand, damage due to pollution and, on the other hand, the kind of biological agents that have affected its stones as well as mortar. The complete analysis of the material, obtained from calcinations of different types of travertine stones extracted from different quarries, has enabled us to establish whether the lime used in mortars could have been obtained from the travertine marbles in the surrounding area. Finally, as a result of the studies conducted, specific mortars have been designed for every particular need in the restoration process ; Postprint (published version)