The term Catholic Monarchs refers to Queen Isabella I of Castile and King Ferdinand II of Aragon, whose marriage and joint rule marked the "de facto" unification of Spain. They were both from the House of Trastámara and were second cousins, being both descended from John I of Castile; on marriage they were given a papal dispensation to deal with consanguinity by Sixtus IV. They married on October 19, 1469, in the city of Valladolid; Isabella was eighteen years old and Ferdinand a year younger. It is generally accepted by most scholars that the unification of Spain can essentially be traced back to the marriage of Ferdinand and Isabella.