Worthy of mention is the fact that both in Christian Hispania, heir of the Hispanic-Roman and Hispanic-Goth tradition and in al-Andalus, institutions were founded with monarchic competencies of the highest level existing at that time. Hence, while in Western Europe the highest formal political rank was held by the Emperor of the Holy Roman Empire, in Christian Spain there were several kings, Alfonso VI and Alfonso VII of León and Castilla in particular, who held the title of Emperor of Spain or of the Spains. In Spanish-Muslim lands, the monarchs of Córdoba took the titles of Emir and Caliph, like their counterparts in the Afro-Asian Islamic universe with centres in Damascus and Baghdad.
The culmination of the Reconquest at the end of the 15th century resulted in the disappearance of the Spanish-Muslim space and the political and territorial convergence of the most important Spanish crowns (Castile and Aragon) under the same monarchs, the Catholic Monarchs, Isabel and Fernando. This merger of monarchies was shortly joined by Navarre, and, with Felipe II, at the end of the following century by the Kingdom of Portugal, thus achieving the full union of the Hispanic or Iberian Peninsula, under a shared Monarchy. At that time, and also later on, in the 17th and 18th centuries, the Spanish Monarchy took on a world-wide dimension with the subsequent inclusion of lands and kingdoms in different continents. The peoples and territories in America were organised like those in Andalusia after the conquests in the times of Fernando III the Saint. As in Andalusia, kingdoms were formed (those of Jaén, Córdoba, Seville, and subsequently Granada) in the Indies with Viceroys as the monarch's delegates in New Spain, Peru and subsequently in New Granada and in el Plata, whereby the King was considered successor to the emperors, as the sculptures of Moctezuma, the last Aztec emperor, and of Atahualpa, the last Inca emperor, located on one of the façades of the Royal Palace in Madrid.
Catholic, the traditional title or form of address granted to the Monarchs of Spain by Pope Alexander VI in 1496 to Fernando, Isabel and their successors, referred in its time to the specific religion professed by the Monarchs and their defence of the Catholic faith, although according to certain interpretations it also inferred their ecumenical and universalist nature at a time in which, for the first time ever in the world, a political power, in this case the Spanish Monarchy, had attained a global dimension, with sovereignty and effective presence in all the continents (America, Europe, Asia, Africa and Oceania) and in the main seas and oceans (the Atlantic, Pacific, Indian and Mediterranean).
The specific titles used by the Kings of Spain were fruit of this accumulation and incorporation process undertaken by the Spanish Monarchy. Together with the short title - King of Spain or of the Spains, which makes summary reference to the Monarchy's place of origin, the grand or long title was used officially in each reign up until the 19th century. Said long title explicitly mentioned the territories and titles with which the Spanish monarch reigned, with which his ancestors had reigned or over which he was considered to have legitimate rights. By way of an example the vast titles of Carlos IV, still in 1805, laid down in the Royal Letter preceding the Novísima Recopilación de las Leyes de España on its enactment: "Carlos by the grace of God, King of Castile, León, Aragon, the Two Sicilies, Jerusalem, Navarre, Granada, Toledo, Valencia, Galicia, Majorca, Minorca, Seville, Sardinia, Córdoba, Corsica, Murcia, Jaén, the Algarve, Algeciras, Gibraltar, the Canary Isles, the East and West Indies, islands and solid land in the Ocean sea; Archduke of Austria; Duke of Burgundy, Brabante and Milan; Count of Hapsburg, Flanders, Tirol and Barcelona; Lord of Vizcaya and of Molina". It should be mentioned that article 56.2 of the current Spanish Constitution indicates that the title of the Head of State "is that of King of Spain (Rey de España) and he can use the others corresponding to the Crown".
As the apex of the monarchic state, in medieval times and in the Old Regime, the Crown enjoyed the utmost and broadest governmental functions and hence a special responsibility both as regards the successes and failures.
Sancho III the Older, King of Navarre, in the 11th century brought together under his throne a substantial part of Christian Spain. Like other medieval Hispanic kings, however, due to the traditional heritage view of the Monarchy, he ordered that his domains be split up upon his death. King Alfonso IX of León was ahead of his times when in 1188 he convened the first parliament in European history engaging the general public, the nobility and the ecclesiasts. Fernando III the Saint merged the kingdoms of Castile and León definitively, giving the Reconquest irreversible drive. Alfonso X the Wise fostered culture and the arts, as well as laying the foundations for legislation and taxation in a new kind of monarchic state. Jaime I of Aragon and his successors strengthened the political union of the territories of the Aragonese Crown and their overseas expansion into the Mediterranean.