In order to automatically extend a treebank of Old French (9 th -13 th c.) with new texts in Old and Middle French (14 th -15 th c.), we need to adapt tools for syntactic annotation. However, these stages of French are subjected to great variation, and parsing historical texts remains an issue. We chose to adapt a symbolic system, the French Metagrammar (FRMG), and develop a lexicon comparable to the Lefff lexicon for Old and Middle French. The final goal of our project is to model the evolution of language through the whole period of Medieval French (9 th -15 th c.).