Constantine IV

Early career

The eldest son of Constans II and Fausta, daughter of patrician Valentinus, Constantine IV had been named a co-emperor with his father in 654, almost certainly in Easter (13 April). His year of birth is unknown, but often given as 650. He became emperor in September 668, when news arrived at Constantinople that Constans II had been assassinated in Sicily. Within seven months of his accession, Constantine IV had dealt with the insurgency with the support of Pope Vitalian, but this success was overshadowed by troubles in the east.

As early as 668 the Caliph Muawiyah I received an invitation from Saborios, the commander of the troops in Armenia, to help overthrow the Emperor at Constantinople. He sent an army under his son Yazid against the Byzantine Empire. Yazid reached Chalcedon and took the important Byzantine center Amorion. While the city was quickly recovered, the Arabs next attacked Carthage and Sicily in 669. In 670 the Arabs captured Cyzicus and set up a base from which to launch further attacks into the heart of the Empire. Their fleet captured Smyrna and other coastal cities in 672. Also, in 672, the Arabs sent a large fleet to attack Constantinople by sea.

In 663, Emperor Constans II relocated the imperial residence to Syracuse, transferring a significant portion of the Byzantine military to Sicily. This move weakened the defenses of Constantinople and left the capital more exposed to Arab attacks. Arab raids into Anatolia had already begun by , shortly after Muʿāwiya I consolidated his control over the Caliphate following a period of internal conflict. One of these expeditions, led by Busr ibn Abī Artāt, reportedly reached the outskirts of Constantinople and plundered nearby settlements.

During this period, the Byzantine military was unable to repel the incursions effectively. The situation encouraged Saborios, the commander of the Armeniac Theme, to rebel against imperial authority with Arab support. Although Saborios died before his plans were realized, Muʿāwiya proceeded with a large-scale campaign intended to pressure the Byzantine Empire.

In the summer of 667, Muʿāwiya dispatched an army under the command of Fadālah ibn ʿUbayd al-Ansarī towards Constantinople, while a fleet led by his son, Yazīd ibn Muʿāwiya, advanced by sea.

The combined forces blockaded Constantinople but did not attempt a major assault during the winter of 667. Instead, they carried out limited raids in the surrounding countryside. By spring of 668, the siege intensified, lasting through early summer. However, shortages of supplies and an outbreak of disease (reportedly smallpox) caused severe losses among the Arab troops. Yazīd eventually lifted the siege and withdrew. The remaining forces established a base at Cyzicus, from which they continued smaller operations in the region until , when they finally returned to Syria.

Succession Crisis and the usurpation of Mizizios (668) The aftermath of the first Arab siege of Constantinople (667–669) coincided with a period of instability within the Byzantine Empire. Emperor Constans II had established his residence in Syracuse several years earlier, leaving the capital under the authority of his son, Constantine IV. When news of the Arab withdrawals from Constantinople failed to reach Sicily, partly due to the continued naval blockade, rumors of the capital's fall spread rapidly.

On 15 July 668, Constans II was assassinated in Syracuse, reportedly by members of his entourage. Following his death, a group of conspirators proclaimed Mizizios, a high-ranking officer in Sicily, as emperor.

Meanwhile, Muʿāwiyah ibn Ḥudayj al-Kindī, governor of Egypt, launched an expedition against Sicily in an attempt to exploit the Byzantine succession crisis. The Arab fleet conducted brief raids on the island, but when Constantine's forces arrived, reportedly with around six hundred ships, the Arabs withdrew without battle. Constantine landed at Syracuse, captured Mizizios, and ordered his execution. The remaining rebels were sent in chains to Constantinople. In November 680 Constantine convened the Sixth Ecumenical Council (also known as the Third Council of Constantinople). The Council reaffirmed the Orthodox doctrines of the Council of Chalcedon in 451. This solved the controversy over monothelitism; conveniently for the Empire, most monothelites were now under the control of the Umayyad Caliphate.

Constantine IV convenes the 3rd Council of Constantinople, miniature from the 12th century Manasses Chronicle. Due to the ongoing conflicts with the Arabs during the 670s, Constantine had been forced to conclude treaties in the west with the Lombards, who had captured Brindisi and Taranto. Suffering from bad health, the Emperor had to leave the army, which panicked and was defeated by the Bulgars. In 681, Constantine was forced to acknowledge the Bulgar state in Moesia and to pay tribute/protection money to avoid further inroads into Byzantine Thrace. but in late 681 Constantine had them mutilated by slitting their noses so they would be considered ineligible to rule.

Constantine IV died of dysentery on 10 July 685.

Family By his wife Anastasia, Constantine IV had at least two sons: Justinian II in 669, who succeeded him as emperor at the age of sixteen. Heraclius 670, known only from an episode in which his father sent locks of his and his brother's hair to Pope Benedict II.

In art and popular culture Constantine IV was portrayed by Iossif Surchadzhiev in the 1981 Bulgarian movie Aszparuh, directed by Ludmil Staikov. Constantine IV is the subject of the song "Imperator" ("Emperor"), released by the Bulgarian heavy metal band Epizod in their 2012 album Moyata molitva ("My prayer").