Isabella I of Castile and Ferdinand II of Aragón are without a shadow of doubt two great personalities in Spanish and European history, and the union of the two, reigning on terms of equality, was an unparalleled circumstance in the Europe of their day.

The importance of these two monarchs and the decisive events in which they played the lead have led succesors and subsequent governors to cast a look back upon their reign and take the splendour of their time as a point of reference. This fact has had a significant influence on the great number of representations that have been made of the Monarchs, of their characteristic symbols, and in short of their important historical period, in the different state documents from the early years of the past century. These are the documents that were designed and created by the Real Casa de la Moneda, (The Spanish Royal Mint), as the National Mint and Printing Office, and as the continuator of the activity carried out by the artisan workshops of former centuries.

The Catholic Monarchs adopted certain devices as their symbols. These have been maintained and even today some can be found in our national coat-of-arms. From Isabella we have the eagle of Saint John holding the arms of the kingdom, to which the sovereign added the motto "sub umbra alarum tuarum protege nos" (protect us beneath the shadow of your wings), due to the devotion of the queen for the Evangelist. The queen also used the emblems of the yoke and the eleven downward arrows that symbolize unity and the empire.

Ferdinand adopted the Gordian knot, alluding to the one Alexander the Great slashed with his sword. It is represented either independently or crossed by Isabella's yoke, with the initial letter "Y" making reference to the queen.

The device of Don Juan Carlos I still preserves the symbols par excellence of the Catholic Monarchs: the yoke and the arrows together with the Gordian knot.