Constantinus I Magnus (in Latin:.
In his early years, Constantine was sent to the Eastern Empire to serve Augustus Diocleus first and then to fight in Britain. In 306, he was proclaimed Augustus and subsequently won a series of civil wars against Marcentius and Licinius, reunifying the Roman Empire in 324. During Constantine's reign, he implemented a series of reforms: politically, he reorganized the government and separated civil and military authorities; Economically, in order to combat inflation, the introduction of solid-phase funds; Militarily, reorganize the Roman army and repel the attacks of the Franks and Goths; In terms of religion, first issued the "Edict of Milan" with Licinie, and then held the Nicene Conference in 325 to vigorously promote Christianity. In 330 AD, Constantine moved his capital to Byzantium and renamed it New Rome, marking the beginning of the founding of Constantinople. In 337, Constantine passed away in Nicomidia and was baptized as a Christian before his death. [3] After death, he was buried in the Church of the Apostles in Constantinople. [9]
Constantine not only granted Christianity legal status and many privileges, but also forcibly adopted the belief in the "Trinity" as the orthodox doctrine, effectively giving Christianity the status of the state religion. [16] He was the first monarch to convert from Rome to Christianity and was revered as Constantinus Magnus.

Early experiences
In 272 or 274 [14] (and in 273 [16] and 282 [2]), Constantine was born in the province of Mercia in the Roman Empire, Nesus (now Nish in eastern Serbia) [14]. [4] His full name is Gaius Flavius Valerius Constantinus (Latin: Gaius Flavius Valerius Constantinus). He is the eldest son of Constantius I Kroll, the western Augustus of the empire (the emperor [8], see the entry tetrarchy), and has a blood relationship with Augustus Claudius II at the end of the third century. [16]
It is said that Constantine's mother Helena was a maid in a small inn, and Constantine was her illegitimate son with Constantius. But this statement was doubted by the British historian Edward Gibbon. Gibbon believed that Helena was the owner of this small inn and her marriage to Constantius was legal. Anyway, when Constantius was appointed Caesar by the Augustus Maximian of the Western Empire in 293, he abandoned Helena and married Theodora, the daughter of Maximian.
Constantine fought with his father since his youth, developing a strong will and a strong physique. After Constantius became Caesar, he was once held as a hostage by Augustus Diocletian of the Eastern Empire, and became a tribune in Diocletian's court. [16] In 302, he served as a military tribune in the Eastern Empire. [2]
In 305, both Diocletian and Maximian abdicated, and Diocletian's successor, Eastern Augustus Galerius, became even more suspicious of the new Western Augustus Constantius and tried to prevent Constantine from returning to his father. [16] Later, Constantine took the opportunity to escape from the east and went to Britain to meet his father and fight against the barbarians in Britain.

Imperial Struggle
On July 25, 306, Constantius passed away. On the same day, the British Legion declared Constantine Augustus at Iborakum (now York, England) in Britain. But Galileus only awarded him the title of Caesar. [3] At this time, after the death of Constantius, Licinius was appointed to take over by Galerius. The son of Maximius, who was supported by some armies, was once appointed by Galerius as the two Caesars, Severus and Daza. The abdicated Maximius, along with Constantine, engaged in a fierce power struggle for the position of Augustus. [5]
In October 306, Maxentius usurped the throne, and Constantine expressed his support. In 307, Severu, stationed in Milan, was killed in a mutiny by his army. In 310 AD, Maximian launched a rebellion while Constantine was away, and was surrounded and annihilated by Constantine's army in Marseille, forcing him to commit suicide.
In 311, Galerius died of illness, and Constantine began to unite with Licinius against Maxentius. [3] He crossed the Alps and defeated the army of Maximentius in the Battle of Turin, occupying Italy. [9]
On October 28, 312, Constantine defeated Maxentius in a decisive battle near the Milvian Bridge on the Tiber River (see entry: Battle of the Milvian Bridge). Maxentius fell into the water and died in his escape. Constantine executed the family of Maxentius and his important followers in order to ward off future troubles. Then, he entered the city of Rome as a winner.

Unified Empire
In 313, Constantine met with Licinius in Mediolan (now Milan, Italy) and agreed to implement a policy of tolerance towards Christians. Licinius agreed. Licinius married Constantine's sister Constantia to strengthen their alliance. Both Augustus simultaneously issued the "Milan Declaration" (see article Milan Edict), which states that Christians and those with other religious beliefs have the right to freely choose their beliefs, and all measures against Christians have been declared invalid. [5] The background is based on the political intention to win the support of Christians and supervise the defense of the Euphrates River.
After the meeting, Licinius led his army to the east to suppress the self proclaimed Augustus of Daya (Gaius Valerius Galerius Maximinus), and completely defeated him in the Battle of Tezralum in 315. As a result, Licinius was in the east, Constantine was in the west, and the situation where both Augustus stood side by side was restored. Constantine was unwilling to follow this dual dominant pattern and constantly expand his power. Li Xini was quite concerned about this, so he violated the agreement at the Milan conference and began to persecute Christians in his jurisdiction. [5]
In the final struggle to achieve unification, Constantine fully demonstrated the strategy and talent of a politician. He strengthened his control over the military, improved military construction, and implemented a policy of religious tolerance in the areas under his rule, greatly strengthening his own strength. [18]
Constantine took the opportunity to attack Licinius. In 316, Constantine seized Licinius' territory in the Balkans. In 323, they attacked the Thrace region of the Eastern Empire. On July 3rd, at the Battle of Adriaburg, he defeated Licinius' 170000 army and made them hide inside the walls of Byzantium. Subsequently, Licinius' fleet was destroyed in the Battle of the Hellespont Strait, and he could only keep the newly promoted Caesar Martinianus on hold. He retreated to Crespolis, but was defeated in the decisive battle on September 18th. Finally, he fled to his old nest of Nicomidia and surrendered under the guarantee of saving his life. However, in 325 AD, Constantine hanged Licinius under the pretext of conspiracy, rebellion, and collusion with barbarians. From then on, Constantine became the only ruler of the Roman world, namely Constantine I.

On May 20, 325, Constantine ordered Cornell of Nicaea to fight against the infidels. [2]
In 326, Constantine visited the west and arrived in Rome to celebrate. But this visit to Rome was unsuccessful because he refused to participate in pagan parades and offended the Roman people. This was the last time Constantine arrived in Rome during his lifetime. [3] [9]
On May 11, 330, Constantine moved the capital of the Roman Empire from Rome to Byzantium and named the city New Rome, but the city was generally named Constantinople after its founder. [3]
Between 332 and 334, Constantine helped the Sarmatians resist the Goths and personally commanded the battle. [2]
Establishment and Death
In order to maintain the continuity of the dynasty, Constantine appointed his eldest son Crispus and second son Constantine II as the emperor's heirs on March 1, 317, and appointed them as Caesars. However, Crispus, who had high hopes, outstanding military achievements, and exceptional abilities, was suddenly executed in 326 on suspicion of having an affair with his stepmother Fausta, who was close to his age, or on suspicion of a major crime that could not be traced. This incident dealt a great blow to Constantine I, and in order to ensure the continuity of the dynasty's rule, he first appointed his third son Constantius II as Caesar in 324, and later appointed his fourth son Constantine I as Caesar in 333. As a result, in the later years of his rule, all three of his sons were designated as heirs to the throne. [18]
Later, Constantine fell ill while preparing for the battle against Persia and was forced to return to Constantinople. In order to prevent conflicts over imperial power between his brothers after his death, Constantine divided the various sons into their respective spheres of influence, with Constantine II controlling the regions of Britain, Gaul, and Spain, Constantius II controlling the regions of Thrace, West Asia, and Black Haiti, and Constantine controlling regions such as Italy, Africa, Dagia, and Macedonia. [4] [18]
On May 22, 337, Constantine passed away in the palace of Ancelona in Nicomidia. At his deathbed, he was baptized as a Christian. After death, he was buried in the royal cemetery of the St. Apostles' Cathedral in Constantinople.

politics
Reforming the bureaucratic system
Constantine's measures in social reform and fiscal policy only inherited and developed the reform system laid by Diocletian. He further strengthened the bureaucratic structure and implemented the division of civil and military power. Constantine continued to advocate for the etiquette of Eastern autocratic monarchs introduced by Diocletian (wearing a crown, subjects having to kneel before the emperor, etc.). In a word, Constantine perfected Diocletian's autocratic monarchy system (see Domina system), which aimed to overcome the economic crisis in Rome by means of open coercion. But it also makes the bloated bureaucratic system even larger. [20]
Strengthening centralization of power
Constantine maintained the new empire division implemented by Diocletian and implemented a policy of separating local civil and military power. [7] Constantine tried to cancel Diocletian's tetrarchy, but the chaos of the imperial situation forced him to appoint his trusted followers as co rulers. After the death of the first Caesar and his eldest son, Crispus, Constantine appointed the three sons born to Fausta as Caesar: Constantine II ruled over Spain, Gaul, and Britain; Constantius II ruled over Asia and Egypt; Constance I ruled over Italy and North Africa. [18] He actually inherited Diocletian's approach.
Constantine's approach actually changed the system of artificial blood relatives in the appointment of heirs to the throne by late Roman Augustus, abandoning the traditional custom of adopting "adopted sons" by reigning Augustus. It can be seen as an important reform of the Roman Augustan inheritance system. Prior to this, although some Augustus of Rome had passed the throne to their immediate relatives, the specific process still did not go beyond traditional practices. In other words, the traditional inheritance system of the Roman Empire has not changed. Constantine's approach was to treat imperial power as a private right of Augustus himself, who was no longer a public servant of imperial citizens. Therefore, imperial power could and must be passed on to descendants with blood relations like private property. [18]
This institutional arrangement maintained the continuity of the dynasty and strengthened the cohesion of the Byzantine Empire, but it could not eradicate the problem of political instability. After the death of Constantine, brotherly fighting broke out within the Roman ruling class. The royal infighting ultimately led to the killing of most of Constantine I's direct blood heirs and male family heirs.

Expand and relocate the capital to Byzantium
In view of the eastward shift of the economic and cultural center of the empire, in 330 AD, the capital was moved to Byzantium and reconstruction and expansion were carried out. The expanded city is known as the "New Rome", commonly known as Constantinople. This is considered by some scholars to be the beginning of the Eastern Roman Empire. [16]
In the construction of the new capital, Constantine first paid attention to the construction of urban defense. He transformed the old walls of the Byzantine city into tall imperial walls and rebuilt the Constantine wall, which was approximately 3000 meters long, on the westernmost side of the new city. The walls of Constantinople, the walls of the imperial city, and the later construction of the walls of Theodosius due to population expansion and defense needs, formed the city defense system of Constantinople from west to east, ensuring the long-term stability of the empire's rule. [22]
finance
Class solidification
The goal of Constantine's fiscal policy is also to obtain stable taxation. The social consequences of its enforcement are the enslavement of various social classes. The edicts issued in 316 and 325 prohibited the upper class (Curia) of urban residents from leaving their place of birth. They cannot be exempted from the obligations of the city for any reason, nor can they be dismissed from civil or military positions. Kuria's obligations have also become a burden that has been passed down from generation to generation. [7]
Constantine's attitude towards laborers was harsher than that of Curia. In the Edict of 332, it was prohibited for slave farmers to flee from one estate to another; The person who takes in another slave farmer should hand him over to the restored owner, and in addition, pay the taxes that the fugitive slave farmer should pay for all the time he stays on his estate. The edict openly stated, "These fleeing slave farmers should be shackled, just like slaves, in order to force them to fulfill their obligations towards privileged free men by punishing them." Constantine also further fixed the handicraftsmen in their respective guilds, forcing them to jointly bear the taxes and corvee levied by the state on the guilds. In 317, an order was issued stating that "the craftsmen of the mint must remain in their current position for the rest of their lives." Some craftsmen who were fixed in the imperial workshops needed to supply the court and army were also branded to prevent escape.

As for the situation of the slaves themselves, it is even more tragic. According to the laws of Constantine, the life of a slave is not guaranteed: if the master lashes the unruly slave to death in order to "correct" his unruly behavior, he is not prosecuted. This actually restored the power of slave directors to intentionally kill slaves, which had been banned as early as the 2nd century. In the past, slaves who attempted to flee to the barbarians were only handed over to their masters after being captured. Now, the law stipulates that they must be exiled to mines, and some even have their legs chopped off. Constantine also officially announced that the poor were allowed to sell their children as slaves. This goes against the fundamental principles of Roman tradition. Prior to this, the last Augustus of the Severus dynasty, Alexander Severus, allowed free people over the age of twenty to sell themselves into slavery, but by the time Diocletian came to power, he ordered a ban on such behavior. Now Constantine went further on the path of deviating from Roman traditional norms than Severus. His decree also confirmed that slave owners had the right to turn so-called "impolite" released slaves, along with their children, back into slaves. [7]
Overall, under the rule of Constantine, the living conditions of the working and ordinary free people deteriorated sharply, and even the freedom and rights of the middle class were deprived. [7] Although he has issued some laws to protect the poor [20], they are rarely implemented due to widespread lawlessness.
Therefore, there is a viewpoint that states: "The final outcome of the crisis of Roman slavery and the crisis of classical civilization is as follows: the implementation of universal slavery for all working people indicates the inevitable demise of this society

Currency reform
In order to combat inflation, Constantine introduced solid-phase coins, a new type of gold coin that became the standard for Byzantine Empire and European currency for over a thousand years.
military affairs
Reforming the military
In the later stage of the Roman Empire, facing the long border line and the invasion of various barbarian tribes around it, Diocletian attempted to establish a joint rule of four emperors to ensure that each monarch was responsible for a section of the border, in order to maintain the continued implementation of the defensive strategy of obstruction. After Constantine ascended the throne, he switched to the strategy of defense in depth. [21]
The strategy of deep defense requires a clear division of labor and cooperation between the main field army and the border defense army, as well as a vast area of depth in the border area that can be used to weaken the enemy's morale, enable the field army to concentrate, and provide conditions for the field army to encircle and annihilate incoming enemies. For this reason, Constantine launched his reform of the military. He completely completed the military reform of dividing the army into border defense forces and inland mobile forces. On the basis of inheriting Diocletian's policy of weakening the Guard and elevating the Senate, these arrogant Guard forces were further disbanded and replaced with reorganized special palace guards. From then on, military power was completely concentrated in the hands of the emperor. The Commander of the Guard lost his jurisdiction over various departments of the palace, was deprived of the command of the army, and eventually became the Chief Executive of the four major districts of the empire.

But the increasingly corrupt social relations of the empire have led to the deterioration of the military's quality. The previous method of granting land to retired soldiers had the social significance of reviving the small landowner class, and has become a simple means of slavery used to force the son of the land receiver to become a soldier. However, the compulsory conscription of the descendants of veterans for military service can only obtain a portion of the source of new recruits, which is far from meeting the needs of expanding the army with additional soldiers. Therefore, the empire began to attract a large number of barbarian people to join the army (including border defense corps, inland mobile corps, and palace guards), greatly accelerating the process of barbarization of the army. Many people from barbarian backgrounds still hold senior positions in the military. [7]
Constantine reformed and reorganized the army, established a imperial guard directly under the emperor, and changed the border defense force into a militia form, forming a field force and garrison capable of resisting Insider threat and barbaric invasion. [2]
Defeat external enemies
Constantine successfully launched an anti tribal movement against the Franks on the Roman border, and the Alamanic, Gothic, and Sarmatian peoples were relocated to territories abandoned by his predecessors during the crisis of the third century AD. In 313, Constantine repelled the Frankish invasion on the western border. Between 332 and 334, Constantine helped the Sarmatians resist the Goths and personally commanded the battle. In 332, the Gothic army of Alaric was defeated in Mercia (northern Bulgaria). Later, angered by the invasion of the Sarmat people, he turned to condone the destruction of Sarmat by the Gothic king Grimir. Finally, the surviving Salmats were allowed to seek refuge within the Roman Empire.