Where did the ideas that made up the Counter-Enlightenment come from? The answer is ultimately the mediaeval idea of Christendom and the model of Church-State relations associated with it.
What was Christendom?
Christendom can be defined as a Christian society which was theorised, and which existed to a greater or lesser extent in practice, in Europe in the high middle ages. Civil society was governed by secular princes headed by the Holy Roman Emperor, while the Church was governed by the bishops of the Catholic Church under the Pope. The Church was superior to the State, and the Pope could therefore depose the Emperor. (Of course, broader definitions are possible - Christendom as the whole Christian world, for example, or mediaeval Christendom including the Byzantine Empire - but the foregoing definition is the one that I am interested in for the purposes of this article.)
The origins of Christendom
The idea of a Christian empire covering the known world derived from the historical example of the later Roman Empire. It was influenced by the idea that it was necessary to preserve the union of the Christian world in preparation for the end times and the second coming of Christ. Another source of inspiration was the prophet Isaiah's utopian vision of the unity of the nations:
And in the last days the mountain of the house of the Lord shall be prepared on the top of mountains, and it shall be exalted above the hills, and all nations shall flow unto it. And many people shall go, and say: Come and let us go up to the mountain of the Lord, and to the house of the God of Jacob, and he will teach us his ways, and we will walk in his paths: for the law shall come forth from Sion, and the word of the Lord from Jerusalem.
The ideal of Christendom was realised pre-eminently in the Holy Roman Empire. The Empire claimed the same universal jurisdiction or dominium mundi as the Church, albeit not wholly successfully. The Pope and Emperor waged a long-running struggle against each other which ended in stalemate, and the authority of the Empire was undermined by the revival of the power of national monarchs (previously diminished by feudalism) in the 12th century. The Empire survived, however, until Napoleonic times: the last Emperor, Francis II, abdicated in 1806.
It is generally said that the first Holy Roman Emperor was Otto I (962-973), though Charlemagne (800-814) had previously reigned over the territories of modern France and Germany as "Emperor of the Romans" (Imperator Romanorum) and "August Emperor ruling the Roman Empire" (Imperator Augustus Romanum gubernans Imperium). There is a clear link here with later titles of the Holy Roman Emperors such as "Ever August Emperor of the Romans" (Romanorum Imperator Semper Augustus).
The term "Holy" seems to have been added to the title of the Empire (Sacrum Imperium) in 1157, during the reign of Frederick I Barbarossa (1155-1190). In 1512, the name "Holy Roman Empire of the German Nation" (Imperium Romanum Sacrum Nationis Germanicae) was formally adopted.
The heyday of the Empire may be located in the mid-11th century, though it was in the 12th century that Christendom arguably reached its zenith as a cultural and social entity. The pontificate of Innocent III (1198-1216) has been identified as a high point. From then, it was downhill all the way to the Reformation.
The theological foundations of Christendom
The existence of twin authorities - the Church and the Empire or State - created a tension which theologians and churchmen grappled with for many centuries. The Church was clearly superior, in an ultimate sense, to the State, but what was the precise nature of the relationship between them?
This is what Pope Innocent III had to say on the subject in his bull Per Venerabilem (1202):
We acknowledge as we are bound, that the right and authority to elect a king (later to be elevated to the Imperial throne) belongs to those princes to whom it is known to belong by right and ancient custom; especially as this right and authority came to them from the Apostolic See, which transferred the Empire from the Greeks to the Germans in the person of Charles the Great [i.e. Charlemagne]. But the princes should recognize, and assuredly do recognize, that the right and authority to examine the person so elected king (to be elevated to the Empire) belongs to us who anoint, consecrate and crown him.
And this is what Boniface VIII had to say a century later in Unam Sanctam:
[I]n this Church and in its power are two swords; namely, the spiritual and the temporal.... Both... are in the power of the Church... but the former is to be administered by the Church but the latter for the Church; the former in the hands of the priest; the latter by the hands of kings and soldiers, but at the will and sufferance of the priest.... [O]ne sword ought to be subordinated to the other, and temporal authority subjected to spiritual power.... [I]t belongs to the spiritual power to establish the terrestrial power and to pass judgement if it has not been good.
The orthodox doctrine on which theologians finally settled was that the State was supreme in the temporal sphere while the Church was supreme in the spiritual sphere, but the Church and the Pope had an "indirect power" (potestas indirecta) to intervene in the temporal sphere where appropriate. I have written further about this elsewhere.
The indirect power theory is closely associated with St Robert Bellarmine (1542-1621), though it was not invented by him. This is how Bellarmine expressed his point of view:
[T]he Pope as Pope directly and immediately has no temporal power but only a spiritual power; nevertheless by reason of his spiritual power he has at least indirectly a power in temporal things, which is a supreme power.
We assert that the Pope, as Pope, even though he does not have any purely temporal power, nonetheless has the supreme power of disposing of the temporal affairs of all Christians so as to order them to their spiritual good.
It may be added that religious liberty in the Christian State was not to be made available to non-Catholics, as authorities such as St Thomas Aquinas taught.
The best-known consequence of the classical theory of Church-State relations was that the Pope claimed the power to depose the Holy Roman Emperor and other sovereigns. Popes Gregory VII and Innocent IV deposed Emperors Henry IV and Frederick II respectively. Popes Innocent III and Boniface VIII also deposed King John of England and King Philip IV of France respectively. This is what Bellarmine had to say on this matter:
In regard of persons, the Pope as Pope cannot by ordinary jurisdiction depose temporal rulers even for a legitimate reason, after the manner in which he deposes bishops, as their ordinary judge; nevertheless as the supreme spiritual ruler, he can change the royal power, taking it away from one and conferring it on another, if this be necessary for the salvation of souls.
Interestingly, this power was disclaimed by the deeply conservative and reactionary Pope Pius IX in 1871, in an address to the Pontificia Accademia di Religione Cattolica:
Although certain Popes have at times exercised their deposing power in extreme cases, they did so according to the public law then in force and by the agreement of the Christian nations who reverenced in the Pope the Supreme Judge of Christ extended to passing judgment even civiliter on princes and individual states. But altogether different is the present condition of affairs and only malice can confound things and times so different.
The Church-State relationship embodied in Christendom also found expression in the liturgy.
Traditionally, the Holy Roman Emperor was crowned in Rome by the Pope. The coronation ritual naturally varied over time, but it included elements both marking the sacred status of the Emperor and emphasising his subjection to the Roman Pontiff. Most famously, he was ordained by the Pope as a deacon or subdeacon, dressed in religious vestments, and carried out clerical functions during the coronation Mass. On the other hand, he swore to protect the Church and to be loyal to the Papacy, and he kissed the Pope's feet.
The Roman coronation ritual fell into disuse after the coronation of Frederick III in 1440 (though Charles V was crowned by the Pope in Bologna in 1530). Thereafter, the Holy Roman Emperor was crowned in his native Germany by German clerics.
The coronation ceremony for the Holy Roman Emperor came to be used for the coronation of Catholic monarchs generally (see some interesting excerpts here). Until 1968, this was the basis of the coronation ceremony in the Pontificale Romanum, the liturgical book containing ceremonies conducted by bishops. It is not clear who was the last Catholic monarch to be crowned in accordance with this rite - perhaps Baudouin I of Belgium in 1951.
Another ceremony which the imperial coronation influenced was the papal coronation, which contains these memorable and famous words at the point where the new pope is crowned:
Receive the tiara adorned with three crowns, and know that you are the Father of Princes and Kings, the Ruler of the World, the Vicar of our Saviour Jesus Christ on earth, to whom is honour and glory for ever.