The arrano beltza ("black eagle" in Basque) is an ancient Basque and Navarre symbol which shows a black eagle upon a yellow background. Today it is mostly, though not exclusively, used by Basque nationalists as a symbol of Euskal Herria, the Basque Country.
Read more about Arrano Beltza: History, Use By Basque Nationalists, Occasional Use By Spanish Nationalists