The Sanfermines were held for the first time on this date. Until then, St. Fermin's day was October 10. Why did they change date? 76 years before, 7 July 1515, three years after the conquest of Navarra, by the integration of the Kingdom of Navarre in the Cortes de Burgos. The bishop of Pamplona, Bernardo Sandoval, wanted to unite the celebration of the Navarros to this event.