Byzantine emperor in the context of "Constantine VIII"

Basil II Porphyrogenitus (Greek: Βασίλειος Πορφυρογέννητος, romanized: Basíleios Porphyrogénnētos; 958 – 15 December 1025), nicknamed the Bulgar Slayer (Greek: ὁ Βουλγαροκτόνος, ho Boulgaroktónos, Bulgarian: Българоубиец), was the senior Byzantine emperor from 976 to 1025. He and his brother Constantine VIII were crowned before their father Romanos II died in 963, but they were too young to rule. The throne thus went to two generals, Nikephoros Phokas (r. 963–969) and John Tzimiskes (r. 969–976) before Basil became senior emperor, though his influential great-uncle Basil Lekapenos remained as the de facto ruler until 985. His reign of 49 years and 11 months was the longest of any Roman emperor.

The early years of Basil's reign were dominated by civil wars against two powerful generals from the Byzantine Anatolian aristocracy: first Bardas Skleros and later Bardas Phokas, which ended shortly after Phokas' death and Skleros' submission in 989. Basil then oversaw the stabilization and expansion of the eastern frontier of the Byzantine Empire and the complete subjugation of the First Bulgarian Empire, its foremost European foe, after a long struggle. Although the Byzantines had made a truce with the Fatimid Caliphate in 987–988, Basil led a campaign against the Caliphate that ended with another truce in 1000. He also conducted a campaign against the Khazar Khaganate that gained the Byzantine Empire part of Crimea and a series of successful campaigns against the Kingdom of Georgia.

Constans II (Greek: Κώνστας, romanized: Kōnstās; 7 November 630 – 15 July 668), also called "the Bearded" (Greek: ὁ Πωγωνᾶτος, romanized: ho Pōgōnãtos), was the Byzantine emperor from 641 to 668. Constans was the last attested emperor to serve as consul, in 642, although the office continued to exist until the reign of Leo VI the Wise (r. 886–912). His religious policy saw him steering a middle line in disputes between the Orthodox and Monothelites by refusing to persecute either and prohibited discussion of the natures of Jesus Christ under the Typos of Constans in 648. His reign coincided with Arab invasions under Umar, Uthman, and Mu'awiya I in the late 640s to 660s. Constans was the first emperor to visit Rome since the fall of the Western Roman Empire in 476, and the last one to visit Rome while the Empire still held it.

The East–West Schism, also known as the Great Schism or the Schism of 1054, is the break of communion between the Catholic Church and the Eastern Orthodox Church since 1054. A series of ecclesiastical differences, theological disputes and geopolitical tensions between the Greek East and Latin West preceded the formal split that occurred in 1054. Prominent among these were the procession of the Holy Spirit (Filioque), whether leavened or unleavened bread should be used in the Eucharist, iconoclasm, the coronation of Charlemagne as emperor of the Romans in 800, the pope's claim to universal jurisdiction, and the place of the See of Constantinople in relation to the pentarchy.

The first action that led to a formal schism occurred in 1053 when Patriarch Michael I Cerularius of Constantinople ordered the closure of all Latin churches in Constantinople. In 1054, the papal legate sent by Leo IX travelled to Constantinople in order, among other things, to deny Cerularius the title of "ecumenical patriarch" and insist that he recognize the pope's claim to be the head of all of the churches. The main purposes of the papal legation were to seek help from the Byzantine emperor, Constantine IX Monomachos, in view of the Norman conquest of southern Italy, and to respond to Leo of Ohrid's attacks on the use of unleavened bread and other Western customs, attacks that had the support of Cerularius. The historian Axel Bayer says that the legation was sent in response to two letters, one from the emperor seeking help to organize a joint military campaign by the eastern and western empires against the Normans, and the other from Cerularius. When the leader of the legation, Cardinal Humbert of Silva Candida, O.S.B., learned that Cerularius had refused to accept the demand, he excommunicated him, and in response Cerularius excommunicated Humbert and the other legates. According to Kallistos Ware, "Even after 1054 friendly relations between East and West continued. The two parts of Christendom were not yet conscious of a great gulf of separation between them ... The dispute remained something of which ordinary Christians in East and West were largely unaware".

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.

John I Tzimiskes (Greek: Ἰωάννης ὁ Τζιμισκής, romanized: Iōánnēs ho Tzimiskēs; born John Kourkouas c. 925 – 10 January 976) was the senior Byzantine emperor from 969 to 976. An intuitive and successful general who married into the influential Skleros family, he strengthened and expanded the Byzantine Empire to include Thrace and Syria by warring with the Rus' under Sviatoslav I and the Fatimids respectively.

Constantine IV (Greek: Κωνσταντῖνος, romanized: Kōnstantīnos, lit. 'Constantinus'); c. 650 – 10 July 685), called the Younger (Greek: ὁ νέος, romanized: ho Néos) and often incorrectly the Bearded (Greek: Πωγωνᾶτος, romanized: Pōgōnãtos) out of confusion with his father, was Byzantine emperor from 668 to 685. His reign saw the first serious check to nearly 50 years of uninterrupted Arab expansion, most notably his successful defence of Constantinople, and the temporary stabilization of the Byzantine Empire after decades of war, defeats, and civil strife. His calling of the Sixth Ecumenical Council saw the end of the monothelitism controversy in the Byzantine Empire; for this, he is venerated as a saint in the Eastern Orthodox Church, with his feast day on September 3.

The coronation (Greek: στέψιμον, romanized: stépsimon, or στεφάνωσις, stephánosis) was the main symbolic act of accession to the throne of a Byzantine emperor, co-emperor, or empress. Founded on Roman traditions of election by the Senate or acclamation by the army, the ceremony evolved over time from a relatively simple, ad hoc affair to a complex ritual.

In the 5th–6th centuries the coronation became gradually standardized, with the new emperor appearing before the people and army at the Hippodrome of Constantinople, where he was crowned and acclaimed. During the same time, religious elements, notably the presence of the patriarch of Constantinople, became prominent in what was previously a purely military or civilian ceremony. From the early 7th century on, the coronation ceremony usually took place in a church, chiefly the Hagia Sophia, the patriarchal cathedral of Constantinople. The association of the coronation ceremony with Constantinople and the Hagia Sophia became so close that even emperors who had been proclaimed, and crowned, outside the capital as military rebels or usurpers, usually repeated their coronation in the capital once they had won power.

Nikephoros II Phokas (Greek: Νικηφόρος Φωκᾶς, romanized: Nikēphóros Phōkâs; c. 912 – 11 December 969), Latinized Nicephorus II Phocas, was Byzantine emperor from 963 to 969. His career, not uniformly successful in matters of statecraft or of war, nonetheless greatly contributed to the resurgence of the Byzantine Empire during the 10th century. In the east, Nikephoros completed the conquest of Cilicia and retook the islands of Crete and Cyprus, opening the path for subsequent Byzantine incursions reaching as far as Upper Mesopotamia and the Levant; these campaigns earned him the sobriquet "pale death of the Saracens."