He spent his leisure and his fortune in the search for documents bearing on the old Basque and Béarnese provinces; and the fruits of his studies in the archives of Bayonne, Toulouse, Pau, Périgord and other cities were embodied in forty-five manuscript volumes, which were sent by his son Gabriel to Colbert. Twenty of these are in the Bibliothèque Nationale of Paris (Coll. Duchesne). In his quest for information, he attempted to scour the files of the Accountancy Chamber or "Comptos" in the Spanish Navarre, but was denied access by the viceroy to prevent his using it against the 1512 Spanish military takeover.