Constantine I in the context of Flavius Constantius

In Christianity, a martyr is a person who was killed for their testimony for Jesus or faith in Jesus. In the years of the early church, stories depict this often occurring through death by sawing, stoning, crucifixion, burning at the stake, or other forms of torture and capital punishment. The word martyr comes from the Koine word μάρτυς, mártys, which means "witness" or "testimony".

At first, the term applied to the Apostles. Once Christians started to undergo persecution, the term came to be applied to those who suffered hardships for their faith. Finally, it was restricted to those who had been killed for their faith. The early Christian period before Constantine I was the "Age of Martyrs". "Early Christians venerated martyrs as powerful intercessors, and their utterances were treasured as inspired by the Holy Spirit."

In the history of Christianity, the first seven ecumenical councils are as follows: the First Council of Nicaea in 325, the First Council of Constantinople in 381, the Council of Ephesus in 431, the Council of Chalcedon in 451, the Second Council of Constantinople in 553, the Third Council of Constantinople from 680 to 681 and finally, the Second Council of Nicaea in 787.

These seven events represented an attempt by Church leaders to reach an orthodox consensus, restore peace and develop a unified Christendom. Among Eastern Christians the Eastern Orthodox, Oriental Orthodox, and Church of the East (Assyrian) churches and among Western Christians the Roman Catholic, Anglican, Utrecht and Polish National Old Catholic, and some Scandinavian Lutheran churches all trace the legitimacy of their clergy by apostolic succession back to this period and beyond, to the earlier period referred to as the Early Church.

The praetorian prefecture (Latin: praefectura praetorio; in Greek variously named ἐπαρχότης τῶν πραιτωρίων or ὑπαρχία τῶν πραιτωρίων) was the largest administrative division of the late Roman Empire, above the mid-level dioceses and the low-level provinces. Praetorian prefectures originated in the reign of Constantine I (r. 306–337), reaching their more or less final form in the last third of the 4th century and surviving until the 7th century, when the reforms of Heraclius diminished the prefecture's power, and the Muslim conquests forced the Eastern Roman Empire to adopt the new theme system. Elements of the prefecture's administrative apparatus, however, are documented to have survived in the Byzantine Empire until the first half of the 9th century.

The Roman Theatre of Mérida is a Roman theatre in the Roman colonia of Emerita Augusta –present-day Mérida, Spain–, capital of the Roman province of Lusitania. Its construction was promoted by the consul Vipsanius Agrippa and was built in 16–15 BCE. It was used for Roman theatrical performances during ancient Rome. Since 1933, it houses the International Festival of Classical Theatre of Mérida [es].

The theatre has undergone several renovations, notably at the end of the 1st century or early 2nd century CE (possibly during the reign of Emperor Trajan), when the current facade of the scaenae frons was erected, and another in the time of Constantine I (between 330 and 340 CE), which introduced new decorative-architectural elements and a walkway around the monument. Following the theatre's abandonment in Late Antiquity, it was slowly covered with earth, with only the upper tiers of seats (summa cavea) remaining visible. In local folklore the site was referred to as "The Seven Chairs", where, according to tradition, several Moorish kings sat to decide the fate of the city.

The Byzantine senate or Eastern Roman senate (Greek: Σύγκλητος, Synklētos, or Γερουσία, Gerousia) was a continuation of the Roman Senate, established in the 4th century by Constantine I. It survived for centuries, but the senate's powers varied greatly during its history and gradually diminished until its eventual disappearance in the 13th century.

The senate of the Byzantine Empire originally consisted of Roman senators who happened to live in the East, or those who wanted to move to Constantinople, and a few other bureaucrats who were appointed to the senate. Constantine offered free land and grain to any Roman senators who were willing to move to the East. When Constantine founded the Eastern senate in Byzantium, it initially resembled the councils of important cities like Antioch rather than the Roman Senate. His son Constantius II raised it from the position of a municipal to that of an imperial body but the senate in Constantinople had essentially the same limited powers as the senate in Rome. Constantius II increased the number of senators to 2,000 by including his friends, courtiers, and various provincial officials.

The civil wars of the Tetrarchy were a series of conflicts between the co-emperors of the Roman Empire, starting from 306 AD with the usurpation of Maxentius and the defeat of Severus to the defeat of Licinius at the hands of Constantine I in 324 AD.

Marcus Aurelius Valerius Maxentius (c. 283 – 28 October 312) was a Roman emperor from 306 until his death in 312. Despite ruling in Italy and North Africa, and having the recognition of the Senate in Rome, he was not recognized as a legitimate emperor by his fellow emperors.

He was the son of former Emperor Maximian and the son-in-law of Emperor Galerius. The latter part of his reign was preoccupied with civil war, allying with Maximinus against Licinius and Constantine. The latter defeated him at the Battle of the Milvian Bridge in 312, where Maxentius, with his army in flight, purportedly perished by drowning in the Tiber river.

Valerius Licinianus Licinius (/lɪˈsɪniəs/; Greek: Λικίνιος; c. 265 – 325) was Roman emperor from 308 to 324. For most of his reign, he was the colleague and rival of Constantine I, with whom he co-authored the Edict of Milan that granted official toleration to Christians in the Roman Empire. He was finally defeated at the Battle of Chrysopolis (AD 324), and was later executed on the orders of Constantine.

The Byzantine Empire's history is generally periodised from late antiquity until the Fall of Constantinople in 1453 AD. From the 3rd to 6th centuries, the Greek East and Latin West of the Roman Empire gradually diverged, marked by Diocletian's (r. 284–305) formal partition of its administration in 285, the establishment of an eastern capital in Constantinople by Constantine I in 330, and the adoption of Christianity as the state religion under Theodosius I (r. 379–395), with others such as Roman polytheism being proscribed. Although the Western half of the Roman Empire had collapsed in 476, the Eastern half remained stable and emerged as one of the most powerful states in Europe, a title it held for most of its existence. Under the reign of Heraclius (r. 610–641), the Empire's military and administration were restructured and adopted Greek for official use instead of Latin. While there was an unbroken continuity in administration and other features of Roman society, historians have often distinguished the Byzantine epoch from earlier eras in Roman history for reasons including the imperial seat moving from Rome to Constantinople and the predominance of Greek instead of Latin.

The borders of the Empire evolved significantly over its existence, as it went through several cycles of decline and recovery. During the reign of Justinian I (r. 527–565), the Empire reached its greatest extent after reconquering much of the historically Roman western Mediterranean coast, including north Africa, Italy, and Rome itself, which it held for two more centuries. During the reign of Maurice (r. 582–602), the Empire's eastern frontier was expanded and the north stabilised. However, his assassination caused a two-decade-long war with Sassanid Persia which exhausted the Empire's resources and contributed to major territorial losses during the Muslim conquests of the 7th century. In a matter of years the Empire lost its richest provinces, Egypt and Syria, to the Arabs.

The Byzantine Greeks, Byzantines or Eastern Romans (Greek: Ῥωμαῖοι, romanized: Rhōmaîoi) were the Greek-speaking people of the Byzantine Empire. They were Chalcedonian Christians who self-identified as Romans throughout Late Antiquity and the Middle Ages. Latin speakers identified them simply as Greeks or with the term Romaei. They were the main inhabitants of the capital Constantinople and lands of the Eastern Roman Empire, such as Asia Minor (modern Turkey), Cyprus, Greece, and portions in the rest of the southern Balkans and southern Italy; they also formed large minorities, or pluralities, in the coastal urban centres of the northern Black Sea coast, Levant, and northern Egypt.

Use of Greek was already widespread in the eastern Roman Empire when Constantine I (r. 306–337) moved its capital to Constantinople, while Anatolia had also been hellenized by early Byzantine times. The empire lost its predominantly non-Greek speaking provinces by the 7th century Muslim conquests and its population was overwhelmingly Greek-speaking by the 8th century. Unlike the early medieval West, the Greek education of the East was more advanced, resulting in widespread basic literacy. Success came easily to Greek-speaking merchants, who enjoyed a strong position in international trade.

The praetorian prefect (Latin: praefectus praetorio; Greek: ἔπαρχος/ὕπαρχος τῶν πραιτωρίων) was a high office in the Roman Empire established by Emperor Augustus in 2 BC. Originating as the commander of the Praetorian Guard, the office gradually acquired extensive legal and administrative functions, with its holders becoming the Emperor's chief aides. Under Constantine I, the office was much reduced in power and transformed into a purely civilian administrative post, while under his successors, territorially defined praetorian prefectures emerged as the highest-level administrative division of the Empire. The prefects again functioned as the chief ministers of the state, with many laws addressed to them by name. In this role, praetorian prefects continued to be appointed by the Eastern Roman Empire (and the Ostrogothic Kingdom) until the reign of Heraclius in the 7th century AD, when wide-ranging reforms reduced their power and converted them to mere overseers of provincial administration. The last traces of the prefecture disappeared in the Byzantine Empire by the 840s.

The term praefectus praetorio was often abbreviated in inscriptions as "PR PR" or "PPO".

Constantine II (Latin: Flavius Claudius Constantinus; 316–340) was Roman emperor from 337 to 340. The son of the emperor Constantine I, he was proclaimed caesar by his father shortly after his birth. He was associated with military victories over the Sarmatians, Alamanni and Goths during his career, for which he was granted a number of victory titles. He held the consulship four times – in 320, 321, 324, and 329.

Constantine I had arranged for his sons to share power with their cousins Dalmatius and Hannibalianus, but this was not accepted by Constantine II and his brothers. As a result, Constantine II's brother Constantius II ordered the killings of numerous male relatives following Constantine I's death, including Dalmatius and Hannibalianus, thus eliminating any possible opponents to the succession of Constantine I's sons. Constantine II then ascended to the throne alongside his two younger brothers, ruling Gaul, Hispania, and Britain. However, his belief in his rights of primogeniture and attempts to exert them over his youngest brother Constans caused conflict, which ended with his death in a failed invasion of Italy in 340. Constans subsequently took control of Constantine's territories, with the latter being subjected to damnatio memoriae.

Flavius Valerius Severus (died September 307), also called Severus II, was a Roman emperor from 306 to 307, and a member of the Tetrarchy. He shared control of the western half of the empire with Constantine I, but spent most of his short reign in a civil war against the usurper Maxentius, who later killed him and took over Italy.

Old St. Peter's Basilica consisted of the church buildings that stood, from the 4th to 16th centuries, where St. Peter's Basilica stands today in Vatican City. Construction of the basilica, built over the historical site of the Circus of Nero, began during the reign of Roman Emperor Constantine I. The name "old St. Peter's Basilica" has been used since the construction of the current basilica to distinguish the two buildings.

The Historia Augusta (English: Augustan History) is a late Roman collection of biographies, written in Latin, of the Roman emperors, their junior colleagues, designated heirs and usurpers from 117 to 284. Supposedly modeled on the similar work of Suetonius, The Twelve Caesars, it presents itself as a compilation of works by six different authors, collectively known as the Scriptores Historiae Augustae, written during the reigns of Diocletian and Constantine I and addressed to those emperors or other important personages in Ancient Rome. The collection, as extant, comprises thirty biographies, most of which contain the life of a single emperor, but some include a group of two or more, grouped together merely because these emperors were either similar or contemporaneous.

The true authorship of the work, its actual date, its reliability and its purpose have long been matters for controversy by historians and scholars ever since Hermann Dessau, in 1889, rejected both the date and the authorship as stated within the manuscript. Major problems include the nature of the sources that it used, and how much of the content is pure fiction. For instance, the collection contains in all about 150 alleged documents, including 68 letters, 60 speeches and proposals to the people or the senate, and 20 senatorial decrees and acclamations.

The Lateran Obelisk (Italian: Obelisco Lateranense; Latin: Obeliscus Constantii) is the largest standing ancient Egyptian obelisk in the world, and it is also the tallest obelisk in Italy. It originally weighed 413 tonnes (455 short tons), but after collapsing and being re-erected 4 metres (13 ft) shorter, now weighs around 300 tonnes (330 short tons). It is located in Rome, in the square across from the Archbasilica of Saint John Lateran and the San Giovanni Addolorata Hospital.

The obelisk was made around 1400 BC in Karnak, Egypt, during the reigns of Pharaohs Thutmose III and Thutmose IV. Roman Emperor Constantine I had it moved to Alexandria in the early 4th century AD, then Constantius II in AD 357 had it shipped to Rome and erected at the Circus Maximus. The obelisk collapsed and broke into pieces sometime after the Circus's abandonment in the 5th century and became buried. It was excavated and restored by Domenico Fontana in the late 1580s, and by the order of Pope Sixtus V was topped with a Christian cross and installed in its present location near the Lateran Palace.

Lucius Caecilius Firmianus Lactantius (c. 250 – c. 325) was an early Christian author who became an advisor to Roman emperor Constantine I, guiding his Christian religious policy in its initial stages of emergence, and a tutor to his son Crispus. His most important work is the Institutiones Divinae ("The Divine Institutes"), an apologetic treatise intended to establish the reasonableness and truth of Christianity to pagan critics.

He is best known for his apologetic works, widely read during the Renaissance by humanists, who called Lactantius the "Christian Cicero". Also often attributed to Lactantius is the poem The Phoenix, which is based on the myth of the phoenix from Egypt and Arabia. Though the poem is not clearly Christian in its motifs, modern scholars have found some literary evidence in the text to suggest the author had a Christian interpretation of the eastern myth as a symbol of resurrection.