Episcopal see in the context of "Mark the Evangelist"

Vatican City, officially the Vatican City State (Italian: Stato della Città del Vaticano; Latin: Status Civitatis Vaticanae), often shortened as the Vatican, is a landlocked sovereign city-state. Ruled by the pope, it is an enclave within Rome and serves as the administrative centre of the Catholic Church. Vatican City is governed by the See of Rome, commonly known as the Holy See, itself a sovereign entity under international law, which maintains its temporal power, governance, diplomacy, and spiritual independence. Vatican is also used as a metonym for the Holy See, which is the central governing body of the Catholic Church and Vatican City, comprising the pope and the Roman Curia. The independent state of Vatican City came into existence in 1929 via the Lateran Treaty between the Holy See and the Kingdom of Italy, which spoke of it as a new creation, not as a vestige of the much larger Papal States (756–1870), which had previously encompassed much of Central Italy.

With an area of 48.99 hectares (121 acres) and a population of about 882 in 2024, it is the smallest sovereign state in the world both by area and by population. It is among the least populated capitals in the world. As governed by the Holy See, Vatican City State is an ecclesiastical or sacerdotal-monarchical state ruled by the pope, who is the bishop of Rome and head of the Catholic Church; the highest state functionaries are all Catholic clergy of various origins. The Holy See dates to early Christianity and is the principal episcopal see of the Catholic Church, which in 2018 had about 1.329 billion baptized Catholics in the world, in the Latin Church and 23 Eastern Catholic Churches. After the Avignon Papacy (1309–1377) the popes have mainly resided at the Apostolic Palace within what is now Vatican City, although at times residing instead in the Quirinal Palace in Rome or elsewhere.

The pope is the bishop of Rome and the head of the worldwide Catholic Church. He is also known as the supreme pontiff, Roman pontiff, or sovereign pontiff. From the 8th century until 1870, the pope was the sovereign or head of state of the Papal States, and since 1929 of the much smaller Vatican City State. From a Catholic viewpoint, the primacy of the bishop of Rome is largely derived from his role as the apostolic successor to Saint Peter, to whom primacy was conferred by Jesus, who gave Peter the Keys of Heaven and the powers of "binding and loosing", naming him as the "rock" upon which the Church would be built. The current pope is Leo XIV, who was elected on 8 May 2025 on the second day of the 2025 papal conclave.

While his office is called the papacy, the jurisdiction of the episcopal see is called the Holy See. The word see comes from the Latin for 'seat' or 'chair' (sede, referring in particular to the one on which the newly elected pope sits during the enthronement ceremony). The Holy See is a sovereign entity under international law; it is headquartered in the distinctively independent Vatican City, a city-state which forms a geographical enclave within the conurbation of Rome. It was established by the Lateran Treaty in 1929 between Fascist Italy and the Holy See to ensure its political and spiritual independence. The Holy See is recognized by its adherence at various levels to international organizations and by means of its diplomatic relations and political accords with many independent states.

The Ecumenical Patriarch of Constantinople (Greek: Οἰκουμενικός Πατριάρχης, romanized: Oikoumenikós Patriárchēs) is the archbishop of Constantinople and primus inter pares (first among equals) among the heads of the several autocephalous churches that comprise the Eastern Orthodox Church. The ecumenical patriarch is regarded as the representative and spiritual leader of the Eastern Orthodox Christians worldwide. The term ecumenical in the title is a historical reference to the Ecumene, a Greek designation for the civilised world, i.e. the Roman Empire, and it stems from Canon 28 of the Council of Chalcedon.

The patriarch's see, the Ecumenical Patriarchate of Constantinople, is one of the most enduring institutions in the world and has had a prominent part in world history. The ecumenical patriarchs in ancient times helped in the spread of Christianity and the resolution of various doctrinal disputes. In the Middle Ages, they played a major role in the affairs of the Eastern Orthodox Church, as well as in the politics of the Orthodox world, and in spreading Christianity among the Slavs. Currently, in addition to the expansion of the Christian faith and the Eastern Orthodox doctrine, the patriarchs are involved in ecumenism and interfaith dialogue, charitable work, and the defense of Orthodox Christian traditions.

Pentarchy (from Ancient Greek Πενταρχία (Pentarchía), from πέντε (pénte) 'five' and ἄρχειν (archein) 'to rule') was a model of Church organization formulated in the laws of Emperor Justinian I (r.  527–565) of the Roman Empire. In this model, the Christian Church is governed by the heads (patriarchs) of the five major episcopal sees of the Roman Empire: Rome, Constantinople, Alexandria, Antioch, and Jerusalem.

The idea came about because of the political and ecclesiastical prominence of these five sees, but the concept of their universal and exclusive authority was attached to earlier Hellenistic-Christian ideas of administration. The pentarchy was first legally expressed in the legislation of Emperor Justinian I, particularly in Novella 131. The Quinisext Council of 692 gave it formal recognition and ranked the sees in order of preeminence, but its organization remained dependent on the emperor, as when Leo the Isaurian altered the boundary of patriarchal jurisdiction between Rome and Constantinople. Especially following Quinisext, the pentarchy was at least philosophically accepted in Eastern Orthodoxy, but in the West, the Rome based patriarchy evolved into the Roman Catholic Church, which would reject the Council as well as the concept of the pentarchy, considering itself the supreme church with universal jurisdiction.

Hagia Sophia, officially the Hagia Sophia Grand Mosque, is a mosque serving as a major cultural and historical site in Istanbul, Turkey. It was formerly a church (360–1453) and a museum (1935–2020). The last of three church buildings to be successively erected on the site by the Eastern Roman Empire, it was completed in AD 537, becoming the world's largest interior space and among the first to employ a fully pendentive dome. It is considered the epitome of Byzantine architecture and is said to have "changed the history of architecture". From its dedication in 360 until 1453 Hagia Sophia served as the cathedral of Constantinople in the Byzantine liturgical tradition, except for the period 1204–1261 when the Latin Crusaders installed their own hierarchy. After the fall of Constantinople in 1453, it served as a mosque, having its minarets added soon after. The site became a museum in 1935, and was redesignated as a mosque in 2020.

The current structure was built by the Byzantine emperor Justinian I as the Christian cathedral of Constantinople between 532–537 and was designed by the Greek geometers Isidore of Miletus and Anthemius of Tralles. It was formally called the Temple of God's Holy Wisdom, (Greek: Ναὸς τῆς Ἁγίας τοῦ Θεοῦ Σοφίας, romanized: Naòs tês Hagías toû Theoû Sophías) the third church of the same name to occupy the site, as the prior one had been destroyed in the Nika riots. As the episcopal see of the ecumenical patriarch of Constantinople, it remained the world's largest cathedral for nearly a thousand years, until the Seville Cathedral was completed in 1520.

Papal primacy, also known as the primacy of the bishop of Rome, is an ecclesiological doctrine in the Catholic Church concerning the respect and authority that is due to the pope from other bishops and their episcopal sees. While the doctrine is accepted at a fundamental level by both the Catholic Church (Eastern and Western) and the Eastern Orthodox Church, the two disagree on the nature of primacy.

English academic and Catholic priest Aidan Nichols wrote that "at root, only one issue of substance divides the Eastern Orthodox and the Catholic Churches, and that is the issue of the primacy." French Eastern Orthodox researcher Jean-Claude Larchet wrote that, together with the Filioque controversy, differences in interpretation of this doctrine have been and remain the primary causes of schism between the Catholic Church and the Eastern Orthodox Church. In the Eastern Orthodox churches, some understand the primacy of the bishop of Rome to be merely one of greater honour, regarding him as primus inter pares ("first among equals"), without effective power over other churches. A prominent 20th century Eastern Orthodox Christian theologian, Fr. Alexander Schmemann, envisioned a primacy that sums up rather than rules over: "Primacy is power, but as power it is not different from the power of a bishop in each church. It is not a higher power but indeed the same power, only expressed, manifested, and realized by one."

The Greek Orthodox Archdiocese of Italy (and Malta from 2005 until the creation of the Exarchate of Malta in 2021), officially the Sacred Orthodox Archdiocese of Italy and Exarchate of Southern Europe (Italian: Sacra Arcidiocesi Ortodossa d'Italia ed Esarcato per l'Europa Meridionale), is a diocese of the Ecumenical Patriarchate of Constantinople with its see in Venice. The diocese was created in 1991.

The current archbishop and exarch is Polykarpos Stavropoulos.

Çermenikë or Çermenika is an upland northeast of Elbasan, in central Albania.

In the Middle Ages, as Tzernikon or Tzernikos it was an episcopal see of the Patriarchate of Constantinople, as a suffragan see of the Archbishopric of Dyrrhachium.