Constantine the Great in the context of "Constantinian dynasty"

The Byzantine Empire, also known as the Eastern Roman Empire, was the continuation of the Roman Empire centred on Constantinople during late antiquity and the Middle Ages. Having survived the events that caused the fall of the Western Roman Empire in the 5th century AD, it endured until the fall of Constantinople to the Ottoman Empire in 1453. The term 'Byzantine Empire' was coined only after its demise; its citizens used the term 'Roman Empire' and called themselves 'Romans'.

During the early centuries of the Roman Empire, the western provinces were Latinised, but the eastern parts kept their Hellenistic culture. Constantine I (r. 324–337) legalised Christianity and moved the capital to Constantinople. Theodosius I (r. 379–395) made Christianity the state religion and Greek gradually replaced Latin for official use. The empire adopted a defensive strategy and, throughout its remaining history, experienced recurring cycles of decline and recovery.

The Western world, also known as the West, primarily refers to various nations and states in Western Europe, Northern America, and Australasia; with some debate as to whether those in Eastern Europe and Latin America also constitute the West. The Western world likewise is called the Occident (from Latin occidens 'setting down, sunset, west') in contrast to the Eastern world known as the Orient (from Latin oriens 'origin, sunrise, east'). Definitions of the "Western world" vary according to context and perspectives; the West is an evolving concept made up of cultural, political, and economic synergy among diverse groups of people, and not a rigid region with fixed borders and members.

Some historians contend that a linear development of the West can be traced from Ancient Greece and Rome, while others argue that such a projection constructs a false genealogy. A geographical concept of the West started to take shape in the 4th century CE when Constantine, the first Christian Roman emperor, divided the Roman Empire between the Greek East and Latin West. The East Roman Empire, later called the Byzantine Empire, continued for a millennium, while the West Roman Empire lasted for only about a century and a half. Significant theological and ecclesiastical differences led Western Europeans to consider the Christians in the Byzantine Empire as heretics. In 1054 CE, when the church in Rome excommunicated the patriarch of Byzantium, the politico-religious division between the Western church and Eastern church culminated in the Great Schism or the East–West Schism. Even though friendly relations continued between the two parts of Christendom for some time, the crusades made the schism definitive with hostility. The West during these crusades tried to capture trade routes to the East and failed, it instead discovered the Americas. In the aftermath of the European colonization of the Americas, primarily involving Western European powers, an idea of the "Western" world, as an inheritor of Latin Christendom emerged. According to the Oxford English Dictionary, the earliest reference to the term "Western world" was from 1586, found in the writings of William Warner.

In modern historiography, the Western Roman Empire were the Roman Empire's western provinces, collectively, during any period in which they were administered separately from the eastern provinces by a separate, independent imperial court. Particularly during the period from AD 395 to 476, there were separate, coequal courts dividing the governance of the empire into the Western provinces and the Eastern provinces with a distinct imperial succession in the separate courts. The terms Western Roman Empire and Eastern Roman Empire were coined in modern times to describe political entities that were de facto independent; contemporary Romans did not consider the Empire to have been split into two empires but viewed it as a single polity governed by two imperial courts for administrative expediency. The Western Empire collapsed in 476, and the Western imperial court in Ravenna disappeared by 554, at the end of Justinian's Gothic War.

Though there were periods with more than one emperor ruling jointly before, the view that it was impossible for a single emperor to govern the entire Empire was institutionalized by emperor Diocletian following the disastrous civil wars and disintegrations of the Crisis of the Third Century. He introduced the system of the Tetrarchy in 286, with two senior emperors titled Augustus, one in the East and one in the West, each with an appointed subordinate and heir titled Caesar. Though the tetrarchic system would collapse in a matter of years, the East–West administrative division would endure in one form or another over the coming centuries. As such, the unofficial Western Roman Empire would exist intermittently in several periods between the 3rd and 5th centuries. Some emperors, such as Constantine I and Theodosius I, governed, if briefly, as the sole Augustus across the Roman Empire. On the death of Theodosius in 395, the empire was divided between his two infant sons, with Honorius as his successor in the West governing briefly from Mediolanum then from Ravenna, and Arcadius as his successor in the East governing from Constantinople.

Constantinople (see other names) was a historical city located on the Bosporus that served as the capital of the Roman (including its eastern continuation), Latin, and Ottoman empires between its consecration in 330 and the formal abolishment of the Ottoman sultanate in 1922. Initially, as New Rome, Constantinople was founded in 324 during the reign of Constantine the Great on the site of the existing settlement of Byzantium and in 330 became the capital of the Roman Empire. Following the collapse of the Western Roman Empire in the late 5th century, Constantinople remained the capital of the Eastern Roman Empire (also known as the Byzantine Empire; 330–1204 and 1261–1453), the Latin Empire (1204–1261), and the Ottoman Empire (1453–1922). In the aftermath of the Turkish War of Independence, the Turkish capital moved to Ankara. Although the city had been known as Istanbul since 1453, it was officially renamed Istanbul on 28 March 1930. As of October 2025, it is the most populous city in Europe, with a population of more than 16 million residents, straddling the Bosporus Strait and lying in both Europe and Asia, and is the financial center of Turkey.

In 324, following the reunification of the Eastern and Western Roman Empires, the ancient city of Byzantium was selected to serve as the new capital of the Roman Empire, and the city was renamed Nova Roma, or 'New Rome', by Emperor Constantine the Great. On 11 May 330, it was renamed Constantinople and dedicated to Constantine. Shortly afterward, in 474 AD, the Great Fire of Constantinople erupted and consequently devastated the region. Constantinople is generally considered to be the center and the "cradle of Orthodox Christian civilization." From the mid-5th century to the early 13th century, Constantinople was the largest and wealthiest city in Europe. The city became famous for its architectural masterpieces, such as Hagia Sophia, the cathedral of the Eastern Orthodox Church, which served as the seat of the Ecumenical Patriarchate; the sacred Imperial Palace, where the emperors lived; the Hippodrome; the Golden Gate of the Land Walls; and opulent aristocratic palaces. The University of Constantinople was founded in the 5th century and contained artistic and literary treasures before it was sacked in 1204 and 1453, including its vast Imperial Library. which contained more than 100,000 volumes. The city was the home of the Ecumenical Patriarch of Constantinople and guardian of Christendom's holiest relics, such as the Crown of Thorns and the True Cross.

Mehmed II (Ottoman Turkish: محمد ثانى, romanized: Meḥemmed-i s̱ānī; Turkish: II. Mehmed, pronounced [icinˈdʒi ˈmehmet]; 30 March 1432 – 3 May 1481), commonly known as Mehmed the Conqueror (Ottoman Turkish: ابو الفتح, romanized: Ebū'l-fetḥ, lit. 'the Father of Conquest'; Turkish: Fâtih Sultan Mehmed), was twice the sultan of the Ottoman Empire from August 1444 to September 1446 and then later from February 1451 to May 1481.

In Mehmed II's first reign, he defeated the crusade led by John Hunyadi after the Hungarian incursions into his country broke the conditions of the truce per the Treaties of Edirne and Szeged. When Mehmed II ascended the throne again in 1451, he strengthened the Ottoman Navy and made preparations to attack Constantinople. At the age of 21, he conquered Constantinople and brought an end to the Byzantine Empire. After the conquest, Mehmed claimed the title caesar of Rome (Ottoman Turkish: قیصر روم, romanized: qayṣar-i rūm), based on the fact that Constantinople had been the seat and capital of the surviving Eastern Roman Empire since its consecration in 330 AD by Emperor Constantine I. The claim was soon recognized by the Patriarchate of Constantinople, albeit not by most European monarchs.

41°53′36″N 12°28′59″E / 41.89333°N 12.48306°E / 41.89333; 12.48306

The Capitolium or Capitoline Hill (/ˈkæpɪtəlaɪn, kəˈpɪt-/ KAP-it-ə-lyne, kə-PIT-; Italian: Campidoglio [kampiˈdɔʎʎo]; Latin: Mons Capitolinus [ˈmõːs kapɪtoːˈliːnʊs]), between the Forum and the Campus Martius, is one of the Seven Hills of Rome.

Byzantine architecture is the architecture of the Byzantine Empire, or Eastern Roman Empire, usually dated from AD 330, when Constantine the Great established a new Roman capital in Byzantium, which became Constantinople, until the fall of the Byzantine Empire in 1453. There was initially no hard line between the Byzantine and Roman Empires, and early Byzantine architecture is stylistically and structurally indistinguishable from late Roman architecture. The style continued to be based on arches, vaults and domes, often on a large scale. Wall mosaics with gold background became standard for the grandest buildings, with frescos a cheaper alternative.

The richest interiors were finished with thin plates of marble or coloured and patterned stone. Some of the columns were also made of marble. Other widely used materials were bricks and stone. Mosaics made of stone or glass tesserae were also elements of interior architecture. Precious wood furniture, like beds, chairs, stools, tables, bookshelves and silver or golden cups with beautiful reliefs, decorated Byzantine interiors.