Ferdinand of Aragon and Isabella of Castile married and united the two kingdoms to form what is now known as the Kingdom of Spain. However, each independently ruled his kingdom, and regional laws retained their governments. The title of "Catholic Kings" is the title Pope Alexander VI granted the Spanish monarchs in 1496, for defending the Catholic dogmas within their realms.
The Surrender of Granada by Francisco Pradilla Ortiz
The Catholic Monarchs set out to reconquer the Iberian Peninsula which was invaded by Muslim Arab Umayyad Caliphate, originating in Damascus. The Arab conquest lasted 15 years between 711 and 726 when they took over the Iberian Peninsula and southern part of France. Nevertheless the whole territory was conquered from the year 720, until 1492. That is, Spain and Portugal were held by Muslims 772 years or eight centuries, with the capital called al-Andalus, in Cordoba, Spain.
Moros and Christians celebrated in many towns and cities of Spain, to commemorate the battles of Reconquista.