Constantine I (27 February 272 – 22 May 337 AD) was a Roman emperor from 306 until he died. He was emperor for longer than any other emperor since Augustus, the first emperor. He was the first ruler of the Roman Empire to be a Christian. He made the old city Byzantium into a new, larger city: Constantinople (now Istanbul, Turkey). The city's name means "City of Constantine" in Greek. He was the son of the emperor Constantius I, and members of their Constantinian dynasty controlled the empire until 364.

Six years after Constantine said that he was emperor, he was fighting for control of Rome with Maxentius at the Battle of Milvian Bridge, a bridge over the Tiber River. When he saw a cross in the sky with the words , he changed his deity from Apollo to Jesus and won the battle or war.

Early life 
Constantine (; ) was born in Naissus (Niš, Serbia). He was born on 27 February. The Calendar of Philocalus and the works of the Latin writer Polemius Silvius both say Constantine was born in 272 or 273. The Latin historian Eutropius wrote the same information. However, the Greek historian and bishop Eusebius of Caesarea wrote that Constantine was born around the year 285.

Constantine's father was Constantius, who later became Roman emperor. Constantine's mother was Helena. She was not from the nobility. The Greek historian Procopius wrote that Helena had come from Drepanon, a city in Bithynia. The Latin theologian Ambrose wrote that Helena was a . Helena and Constantius may not have married, and Helena may have been Constantius's concubine.

Constantine was a military tribune in the Roman army by 293, the year his father became caesar (a junior Roman emperor) on 23 March.

Constantius and the other caesar Galerius each became augustus (a more senior Roman emperor) on 1 May 305. On that day, the emperors Diocletian and Maximian retired. Maximinus Daza and Valerius Severus each became caesar.

Emperor

306–310 
The Consularia Constantinopolitana says that Constantius I died on 25 July 306 in Eboracum (York, England). There, on the same day, the army of Constantius made Constantine augustus. (Later, around August 306, the augustus Galerius agreed that Constantine was caesar, but not that he was augustus.) Roman Egypt accepted Constantine was an emperor.

In autumn 306 or early the next year, Constantine made a military campaign against the Franks. Constantine said that he was Roman consul for the first time in 307. However, the Roman provinces that other emperors controlled did not accept that Constantine was consul. Constantine may have been in Roman Britain again in 307.

Maximian and Constantine may have met at Augusta Treverorum (Trier, Germany) in 307, possibly in late summer. Maximian made Constantine augustus. Constantine married Maximian's daughter Fausta. (This could have been in late summer, September, or as late as 25 December. Historians are not in agreement about the date.) At the start of his reign, only the lands that Constantine controlled accepted Constantine as augustus. Then, the lands that Maximian's son Maxentius controlled also accepted that Constantine was an augustus.

In 308 Constantine fought a war against the Bructeri. In November 308, the emperors Diocletian, Maximian, and Galerius met at Carnutum (Petronell-Carnuntum, Austria) and agreed that Constantine was a caesar. Constantine himself continued to say that he was an augustus. The Latin writer Lactantius wrote that in 309, Constantine got the title in . The Roman provinces that Galerius controlled said that Constantine was Roman consul for the first time in 309, but the provinces Constantine and Maxentius controlled did not accept this.

In 310, probably on the 1 May, Galerius made Maximinus Daza augustus. From this time, the whole empire started to agree that Constantine was an augustus as well. In summer 310, Constantine again fought a military campaign against the Franks. A war between Constantine and Maximian began. Maximian was at Massilia (Marseille, France) when Constantine took control of the city, probably in around July 310. Then Maximian died, probably by suicide.

On 25 July 310, it was Constantine's fifth anniversary festival as emperor (his ). At that time, Constantine gave himself the name in . Constantine said that his father Constantius had been part of the family of the emperor Claudius Gothicus. This was fiction.

310–315 
On 30 April 311, the augustus Galerius made a edict. The Edict of Serdica mostly ended the persecution of Christianity in the Roman Empire. At the start of May, Galerius died. Constantine was Roman consul for the second time in 312.

Constantine was consul for the third time in 313. Constantine fought a civil war with Maxentius. The Calendar of Philocalus says that the Battle of the Milvian Bridge happened on the 28 October 313. In this battle, Constantine's army overcame the army of Maxentius. Maxentius died in the battle. The Latin writer Lactantius wrote about these events. After the battle, Constantine went across the Tiber River and took control of Rome itself. The Calendar of Philocalus says that Constantine went into the city on 29 October, and that there was a festival for two days.

After 18 January 313, Constantine was in Mediolanum (Milan, Italy). There Constantine met his co-emperor, Licinius, in January or February. Either in autumn 313 or during the first half of 314, Constantine travelled to Britain. On 1 August 314 in the city of Arelate (Arles, France), the Council of Arles started (a meeting of bishops. Constantine was consul for the fourth time in 315. In the first half of 315, Constantine probably had success in a military campaign he fought against the Goths and Sarmatians.

The Calendar of Philocalus says that Constantine came again to Rome in July 315. There was a ceremony (an ) when Constantine came to the city. The Calendar says that there was a festival for two days. Constantine got the . On 25 July 315, it was Constantine's tenth anniversary as emperor (his ).

315–320 
On 27 September 315 Constantine went away from Rome. There was another ceremony (a ) when Constantine went out of the city. At some time, Constantine fought a civil war with his co-emperor Licinius. The Calendar of Philocalus says that Constantine's army overcame Licinius's army at the Battle of Cibalae on 8 October 314, but historians are not in agreement about the date. It may have been in 316. After this civil war, Constantine and Licinius made peace. This was either at the end of 314 or in January 317. As part of the agreement, Constantine got from Licinius the Roman provinces next to the Danube. (Licinius kept Thracia however.)

The Consularia Constantinopolitana and the Chronicon Paschale both say Constantine and Licinius chose co-emperors on 1 March 317. Constantine and his co-emperor made their three sons their junior co-emperors (their ). Crispus and Constantine II (Constantine's sons) and Licinius II (Licinius's son) were each made caesar at Serdica (Sofia, Bulgaria). Constantine was Roman consul for the fifth time in 319. He was consul for the sixth time in 320. On the 25 July 320, it was Constantine's fifteenth anniversary as emperor (his ).

320–325 
In 321, it was the fifth anniversary of Crispus, Constantine II, and Licinius II as emperors (each caesar's ). In summer 322, Constantine won a military victory against the Sarmatians. At the start of 323, Constantine fought a war against the Goths.

In 324, Constantine and Crispus fought another war against their co-emperor Licinius. The Consularia Constantinopolitana says that Constantine's army overcame the army of Licinius in a battle near Hadrianopolis (Edirne, European Turkey) on 3 July 324. Constantine's armies again overcame Licinius's soldiers at the Battle of Chrysopolis. The Consularia Constantinopolitana says that this battle was on the 18 September 324. Licinius and Licinius II both retired from being emperors. On 8 November that year, Constantine made his son Constantius II caesar. At that time, all Constantine's co-emperors were Constantine's own children (the  Crispus, Constantine II, and Constantius II).

On 20 May 324 at Nicaea (İznik, Turkey) the Council of Nicaea started. This meeting of bishops ended on 19 July 325. The Greek historian Socrates Scholasticus wrote about these events. The Chronicle of the Latin theologian Jerome and the Chronicon Paschale both say that on 25 July 325, it was Constantine's twentieth anniversary festival as emperor (his ) at Nicomedia (İzmit, Turkey).

325–330 
Constantine was Roman consul for the seventh time in 326. The Consularia Constantinopolitana says that in around March 326, Constantine executed his oldest son, the caesar Crispus. The Calendar of Philocalus says that on 18 July 326 (or the 21 July) Constantine again came to Rome. When he came to the city there was another  ceremony. Jerome wrote that on 25 July 326, it was Constantine's twentieth anniversary festival as emperor (his ) in Rome. (326 was the second year in which Constantine had a festival for the same twentieth anniversary.) Jerome's Chronicle and the Chronicon Paschale both say that Constantine set up the city of Helenopolis on 7 January 327. Constantine was consul for the eighth time in 329. The year was the last time Constantine was consul. The Consularia Constantinopolitana says that on 11 May 330, Constantine was in Byzantium. On that day, Constantine dedicated again the city. After that, Byzantium had the name Constantinople (; ).

330–335 
The Consularia Constantinopolitana says that on 25 December 333, Constantine made his youngest son, Constans, his caesar. They were probably at Constantinople then. In 333 or 334, Calocaerus started a rebellion in Cyprus. The Consularia Constantinopolitana says that the Romans forced the Sarmatians out of the Banat area around the Danube in 334.

Around 335, Shapur II's armies attacked Armenia, as part of the Roman–Persian Wars. Shapur's Sasanian Empire sent Narses to invade Armenia, but the attack did not have success and Narses died. The Consularia Constantinopolitana and the Chronicon Paschale both say that on 25 July 335, it was Constantine's thirtieth anniversary festival as emperor (his ) at Constantinople. Eusebius of Caesarea gave a speech at the festival.

335–337 
On the 18 September 335, Constantine made Dalmatius caesar. Constantine probably made Hannibalianus "King of Kings and of the Pontic people" () on the same day. Eusebius of Caesarea's Life of Constantine says that a Persian embassy from the Sasanian Empire came to Constantine at Constantinople not long after the festival of Easter. Constantine had been at Constantinople on Easter (3 April 337).

Death 
Eusebius of Caesarea's Life of Constantine says that Constantine died at Ancyrona, near Nicomedia (İzmit, Turkey). He died on 22 May 337.

Religion 
 Constantine was the first Christian Roman emperor. His rule changed the Christian Church greatly. In February 313, Constantine met with Licinius in Milan where they made the Edict of Milan. The edict said that Christians could believe what they wanted. This stopped people from punishing Christians, who had often been martyred, or killed for their faith. It also returned the property which had been taken away from them. In 311, Galerius had made a similar edict, though it did not return any property to them. In pagan Rome before this, it had been against the law to practise Christianity, and Christians had often been tortured or killed.  Constantine protected them.  He went on to organize the whole Christian Church at the First Council of Nicea, even though he himself did not get baptized until near the end of his life.

Constantine did not support Christianity alone.  After winning the Battle of the Milvian Bridge, he built the Arch of Constantine) to celebrate, but the arch was decorated with pictures of sacrifices to gods like Apollo, Diana, or Hercules.  It had no Christian symbolism.  In 321, Constantine said that Christians and non-Christians should all join the "day of the sun" (the eastern sun-worship which Aurelian had helped him introduce). His coins also had symbols of the sun-cult until 324. Even after pagan gods disappeared from the coins, Christians symbols never appeared on the coin, either. Even when Constantine dedicated the new city of Constantinople, he was wearing the Apollonian sun-rayed Diadem.

References

Other websites 
 
 
Letters of Constantine: Book 1, Book 2, & Book 3
Encyclopaedia Britannica, Constantine I
12 Byzantine Rulers by Lars Brownworth of Stony Brook School (grades 7–12). 40 minute audio lecture on Constantine.
Constantine I in the 1911 Encyclopædia Britannica
Constantine the Great A site about Constantine the Great and his bronze coins emphasizing history using coins, with many resources including reverse types issued and reverse translations.
House of Constantine bronze coins Illustrations and descriptions of coins of Constantine the Great and his relatives.
BBC North Yorkshire's site on Roman York, Yorkshire and Constantine the Great 
 This list of Roman laws of the fourth century shows laws passed by Constantine I relating to Christianity.
 Professor Edwin Judge discusses Constantine's legacy for a Centre for Public Christianity vodcast 

 Constantine's time in York on the 'History of York'

272 births
337 deaths
Byzantine Emperors