Caesaropapism is the idea of combining the social and political power of secular government with religious power, or of making secular authority superior to the spiritual authority of the Church; especially concerning the connection of the Church with government. Justus Henning Böhmer (1674-1749) may have originally coined the term caesaropapism (Cäseropapismus). Max Weber (1864-1920) wrote: "a secular, caesaropapist ruler... exercises supreme authority in ecclesiastic matters by virtue of his autonomous legitimacy". According to Weber, caesaropapism entails "the complete subordination of priests to secular power."
In an extreme form, caesaropapism is where the head of state, notably the emperor ("Caesar", by extension a "superior" king), is also the supreme head of the church (pope or analogous religious leader). In this form, caesaropapism inverts theocracy (or hierocracy in Weber), in which institutions of the church control the state. Both caesaropapism and theocracy are systems in which there is no separation of church and state and in which the two form parts of a single power-structure.
Caesaropapism's chief example is the authority that the Byzantine (East Roman) Emperors had over the Church of Constantinople and Eastern Christianity from the 330 consecration of Constantinople through the tenth century. The Byzantine Emperor would typically protect the Eastern Church and manage its administration by presiding over ecumenical councils and appointing Patriarchs and setting territorial boundaries for their jurisdiction. The Emperor exercised a strong control over the ecclesiastical hierarchy, and the Patriarch of Constantinople could not hold office if he did not have the Emperor's approval. Such Emperors as Basiliscus, Zeno, Justinian I, Heraclius, and Constans II published several strictly ecclesiastical edicts either on their own without the mediation of church councils, or they exercised their own political influence on the councils to issue the edicts. According to Metropolitan Kallistos Ware, the historical reality of caesaropapism stems from the confusion of the Byzantine Empire with the Kingdom of God and the zeal of the Byzantines "to establish here on earth a living icon of God's government in heaven."
However, Caesaropapism "never became an accepted principle in Byzantium." Several Eastern churchmen such as John Chrysostom, Patriarch of Constantinople and Athanasius, Patriarch of Alexandria, strongly opposed imperial control over the Church, as did Western theologians like Hilary of Poitiers and Hosius, Bishop of Córdoba. Saints, such as Maximus the Confessor, resisted the imperial power as a consequence of their witness to orthodoxy. In addition, at several occasions imperial decrees had to be withdrawn as the people of the Church, both lay people, monks and priests, refused to accept inventions at variance with the Church's customs and beliefs. These events show that power over the Church really was in the hands of the Church itself - not solely with the emperor.
Caesaropapism was most notorious in the Tsardom of Russia when Ivan IV the Terrible assumed the title Czar in 1547 and subordinated the Russian Orthodox Church to the state. This level of caesaropapism far exceeded that of the Byzantine Empire and was taken to a new level in 1721, when Peter the Great replaced the patriarchate with a Holy Synod, making the church a department of his government.
Justinian I conquered the Italian peninsula in the Gothic War (535-554) and appointed the next three popes, a practice that would be continued by his successors and later be delegated to the Exarchate of Ravenna. The Byzantine Papacy was a period of Byzantine domination of the papacy from 537 to 752, when popes required the approval of the Byzantine Emperor for episcopal consecration, and many popes were chosen from the apocrisiarii (liaisons from the pope to the emperor) or the inhabitants of Byzantine Greece, Byzantine Syria, or Byzantine Sicily.
During the dispute between Henry VIII and Pope Clement VII over Henry's wish to have his marriage to Catherine of Aragon annulled, the English Parliament passed the Act in Restraint of Appeals (1533). It stated
Where by divers sundry old authentic histories and chronicles it is manifestly declared and expressed that this realm of England is an empire, and so hath been accepted in the world, governed by one supreme head and king, having the dignity and royal estate of the imperial crown of the same.
The next year Parliament passed the First Act of Supremacy (1534) that explicitly tied the head of church to the imperial crown:
The Crown of Ireland Act, passed by the Irish Parliament in 1541 (effective 1542), changed the traditional title used by the Monarchs of England for the reign over Ireland, from Lord of Ireland to King of Ireland and naming Henry head of the Church of Ireland, for similar reasons.
During the reign of Mary I, the First Act of Supremacy was annulled, but during the reign of Elizabeth I the Second Act of Supremacy, with similar wording to the First Act, was passed in 1559. During the English Interregnum the laws were annulled, but the acts which caused the laws to be in abeyance were themselves deemed to be null and void by the Parliaments of the English Restoration.
When Elizabeth I restored royal supremacy, she replaced the title "Supreme Head" with that of "Supreme Governor", a change both conciliatory to English Catholics on a political level and reflecting a shift toward a more metaphysically and theologically modest stance involving only a claim to supreme authority over the Church of England's conduct in temporal matters. Since then, the monarchs of England, of Great Britain, and of the United Kingdom have claimed the "Supreme Governor" status as well as the title of Defender of the Faith (which was originally bestowed on Henry VIII by Pope Leo X but later revoked by Pope Paul III, as that was originally an award for Henry's defence of Catholicism).
Weber's formal definition of caesaropapism in Economy and Society reads as follows: 'a secular, caesaropapist ruler... exercises supreme authority in ecclesiastic matters by virtue of his autonomous legitimacy.
Caesaropapism entails 'the complete subordination of priests to secular power,' and it essentially means that church matters have become part of political administration [...].