[2] The adjective "Byzantine", derived from Byzantion (Byzantium in Latin), the name of the Greek settlement Constantinople was established on, was only used to describe the inhabitants of the city; it did not refer to the Empire, called Romanía ("Romanland") by its citizens.

[18] Valens's successor, Theodosius I (r. 379–395), restored political stability in the east by allowing the Goths to settle in Roman territory;[19] he also twice intervened in the western half, defeating the usurpers Magnus Maximus and Eugenius in 388 and 394 respectively.

[21] He was the last emperor to rule both the western and eastern halves of the empire;[22] after his death, the West was destabilised by a succession of "soldier-emperors", unlike the East, where administrators continued to hold power.

[25] After Leo I (r. 457–474) failed in his 468 attempt to reconquer the west, the warlord Odoacer deposed Romulus Augustulus in 476, killed his titular successor Julius Nepos in 480, and the office of western emperor was formally abolished.

[30] Following his accession in 527, the law-code was rewritten as the influential Corpus Juris Civilis and Justinian produced extensive legislation on provincial administration;[31] he reasserted imperial control over religion and morality through purges of non-Christians and "deviants";[32] and having ruthlessly subdued the 532 Nika revolt he rebuilt much of Constantinople, including the original Hagia Sophia.

[40] The Sasanian wars restarted during the same year, and continued until the emperor Maurice finally emerged victorious in 591; by this time, the Avars and Slavs had repeatedly invaded the Balkans, causing great instability.

[49] The outbreak of the First Fitna in 656 gave Byzantium breathing space, which it used wisely: some order was restored in the Balkans by Constans II (r. 641–668),[50] and the administrative reorganisation implemented by him known as the "theme system", which allocated troops to defend specific provinces.

[51] Constantine IV (r. 668–685) repelled the Arab efforts to capture Constantinople in the 670s using the recently rediscovered Greek fire,[52] but suffered a reversal against the Bulgars, who soon established an empire in the northern Balkans.

[54] Justinian II sought to build on the stability secured by his father Constantine but was overthrown in 695 after attempting to exact too much from his subjects; over the next twenty-two years, six more rebellions followed in an era of political instability.

[56] Leo and his son Constantine V (r. 741–775), two of the most capable Byzantine emperors, withstood continued Arab attacks, civil unrest, and natural disasters, and reestablished the state as a major regional power.

[57] Leo's reign produced the Ecloga, a new code of law to succeed the one created by Justinian II,[58] and continued to reform the "theme system" in order to lead offensive campaigns against the Muslims, culminating in a decisive victory in 740.

[59] Constantine overcame an early civil war against his brother-in-law Artabasdos, made peace with the new Abbasid Caliphate, campaigned successfully against the Bulgars, and continued to make administrative and military reforms.

[80] His son and successor died young; under two soldier-emperors, Nikephoros II (r. 963–969) and John I Tzimiskes (r. 969–976), the Roman army claimed numerous military successes, including the conquest of Cilicia and Antioch, and a sensational victory against Bulgaria and the Kievan Rus' in 971.

[83] Basil, who for unknown reasons never married or had children, subsequently refused to delegate any authority: he sidelined the military establishment by taking personal command of the army and promoting officers loyal to him.

[89] This political instability, regular budget deficits, a string of expensive military failures, and other problems connected to over-extension led to substantial issues in the empire;[90] its strategic focus moved from maintaining its hegemony to prioritizing defence.

[92] The year 1071 brought two consequential reverses: Bari, the last remaining Byzantine settlement in Italy, was captured by the Normans, while the Seljuks won a decisive victory at the Battle of Manzikert, taking the emperor Romanos IV Diogenes prisoner.

[103] Through a combination of diplomacy and bribery, he cultivated a ring of allies and clients around the empire: the Turks of the Sultanate of Rum, the Kingdom of Hungary, the Cilician Armenians, Balkan princes, Italian and Dalmatian cities, and most importantly Antioch and the Crusader States, marrying one of their princesses in 1161.

[180] Mercenary armies further fueled political divisions and civil wars, these led to a collapse in the Empire's defence, and resulted in significant losses of territories such as Italy and the Anatolian heartland in the 11th century.

[265] Despite these challenges, the empire's mixed economy (characterised by state interventions, public works, and market liberalisation)[266] remained a model of medieval economic adaptability, even as it deteriorated under external pressures.

[317] The early 6th-century reign of Justinian I saw systemic developments: religious art came to dominate, while once-popular public marble and bronze monumental sculpture fell out of favor due to pagan associations.

[322] Other costly objects included illuminated manuscripts, which were lavishly illustrated for a wide range of texts, and silks, often dyed in the prized imperial purple; both became highly popular in Western Europe.

[326] Iconoclasts condemned their use, likening them to pagan idolatry and ascribing recent Umayyad defeats as divine retribution for their use, while iconophile supporters eventually prevailed, maintaining their essential use for veneration, considered distinct from worship, and found precedent in Gospel references.

[328] Subjects and styles became standardised, particularly cross-in-square churches, and already-existing frontality and symmetry evolved into a dominant artistic aesthetic, observable in the small Pala d'Oro enamel and the large mosaics of the Hosios Loukas, Daphni, and Nea Moni monasteries.

[330] As smaller Palaeologan artworks (1261–1453) gained relic status in Western Europe—many looted in the 1204 Fourth Crusade—they greatly influenced the Italo-Byzantine style of Cimabue, Duccio, and later Giotto; the latter is traditionally regarded by art historians as the inaugurator of Italian Renaissance painting.

[338] A new generation (c. 1000–1250), including Symeon, Michael Psellos and Theodore Prodromos, rejected the Encyclopedist emphasis on order, and were interested in individual-focused ideals variously concerning mysticism, authorial voice, heroism, humor and love.

[351] By the Palaiologan period, the dominance of strict compositional rules lessened and John Koukouzeles led a new school which favoured a more ornamental "kalophonic" style which deeply informed post-empire Neo-Byzantine music.

[363] Military innovations included the riding stirrup which provided stability for mounted archers and dramatically transformed the army; a specialised type of horseshoe; the lateen sail, which improved a ship’s responsiveness to wind; and Greek fire—an incendiary weapon capable of burning even when doused with water, first appearing around the time of the Siege of Constantinople (674–678).

[367] As the sole sovereign Orthodox state, Russia developed the Third Rome doctrine, emphasising its cultural heritage as distinct from Western Europe, because the latter had inherited much of the Empire's secular learning.

[375] The Byzantine Empire distinctively blended Roman political traditions, Greek literary heritage, and Christianity, creating the civilisational framework that laid the foundation for medieval Europe.

[376] The Empire preserved European civilisation by acting as a shield against eastern forces such as the Persians, Arabs, and various Steppe peoples (Huns, Avars, Bulgars, Pechenegs, Cumans, and Turks).