The nativity triptych is a rarity of European medieval art. A portable altar, in silver and gilded silver, with 1.30m in height by 1.50m in width. The nativity triptych is shrouded in mystery: was it ordered by D. João I of Portugal after the victory of Aljubarrota, where the Portuguese defeated the Spanish in just half an hour and with a third of the men, or did it belong to D. João I of León and Castile who left it behind in the flight from the Battle?
