This long-term research project is based on the data-mining of the Llibres d'Esposalles conserved at the Archives of the Barcelona Cathedral, an extraordinary data source comprising 244 books of marriage licenses records. It covers about 550.000 unions from over 250 parishes of the Diocese between 1451 and 1905. Its impeccable conservation is a miracle in a region where parish archives have undergone massive destruction. The books include data on the tax posed on each couple depending on their social class, on an eight-tiered scale. These data allow for research on multiple aspects of demographic research, especially on the very long run, such as: population estimates, marriage dynamics, cycles, and indirect estimations for fertility, migration and survival, as well as socio-economic studies related to social homogamy, social mobility, and transmission of social and occupational position. Being continuous over five centuries, the source constitutes a unique instrument to study the dynamics of population distribution, the expansion of the city of Barcelona and the constitution of its metropolitan area, as well as the chronology and the geography in the constitution of new social classes.To this end, a digital library and a database, the Barcelona Historical Marriages Database (BHiMaD), are to be created and completed. An ERC-AG will help doing so while undertaking the research analysis of the database in parallel.The research team, at the U. Autònoma de Barcelona, involves researchers from the Center for Demo-graphic Studies and the Computer Vision Center experts in historical databases and computer-aided recognition of ancient manuscripts. 5CofM will serve the preservation of the original “Llibres d’Esposalles” and unlock the full potential embedded in the collection.