Diocles (full name Gaius Aurelius Valerius Diocletian, Latin: Gaius Aurelius Valerius Diocletian, 244-312 AD), formerly known as Diocles, was the Roman Emperor who reigned from November 20, 284 to May 1, 305 AD. It ended the third century crisis of the Roman Empire (235-284) and established a four emperor co governance system, making it the main political system in the later period of the Roman Empire. Its reforms allowed the Roman Empire to continue its rule over various regions within its borders, at least for several centuries in the eastern region. He removed too many remnants of the Roman Republic for the Roman Empire, and in the end, like the ancient Roman politician Cincinnatius, retired to the countryside.
There are two versions of his situation in his later years. Most pagan historians believe that he lived peacefully through his later years, while Christian historians mostly believe that he went insane and died tragically in his later years due to witnessing the destruction of his four emperor co governance system and the destruction of various achievements.

background of times
The Roman Empire, which once dominated the world, finally entered an unprecedented period of chaos after the end of the Severus dynasty, known as the "Third Century Crisis". The ruling group was plagued by constant internal turmoil and incessant fighting, while slaves and peasants also demonstrated their political power through repeated uprisings.
After Aurelian of Illyria (reigned 270-275) came to power, he adopted a method of absorbing a large number of barbarians into the Roman army, beginning the process of eliminating internal strife and restoring unity. The completion of this process marked the beginning of a new phase of development in Rome, marked by the rise of another important figure - Diocletian.
Early experiences
Diocletian's father was a released slave in Illyria Sarona. Sarona is the capital of the Sarmatian province located in the eastern Adriatic Sea. This is the largest city in the region and a wealthy region that relies on trade, agricultural income, and silver mining.
Dai Keli first joined the army as a son of a lower class working class and rose up in the army.
At that time, during the crisis of the third century, people from lower backgrounds actually had higher opportunities than in the past. Since the tyrant Karakara abolished the tradition that soldiers of the legion must be held by citizens, all types of groups living within the empire can join the army. Dai Kelixian, who chose to join the army, quickly revealed his excellent talent. [1]
By 284, Diocletian had accumulated military achievements and been promoted to the position of captain of the SS of the Roman Empire's leader, Carus.
In 284 AD, Carlos sent one of his sons, Calinus, to suppress local resistance in Gaul, while he himself led another son, Numelianus, on an expedition to Persia. On the way back, the shadow of murder shrouded in the luxurious procession of the F ü hrer. Carlos died mysteriously for various reasons, but the most likely one was murder. His son Numelianus succeeded as the F ü hrer on the spot, but was assassinated a month later when the army marched to Nicomidia in Asia Minor. Captain Apel of the Guard blocked the news of the death, but the foul smell emanating from the body still made the soldiers aware of the result. So, the captain of the SS, Dai Keli, first rose up to expose Apel's crime of killing two leaders in a row, and killed him in a fight. As a result, Diocletian was elected as the new head of state.
At the same time, Calinus in Gaul also announced his succession as the head of state, and the two sides engaged in a decisive battle. Calinus was killed by his subordinates during the battle, and Diocletian became the only ruler of the empire.

Emperor's career
Since the establishment of the system of heads of state by Octavian, the Roman ruling system began to transition from a republic to an absolute monarchy, and Diocletian was the last to complete this process. Under his rule, the Senate was stripped of its last practical power and became a mere decoration of honor. He changed the title of the Chancellor to Dominius (meaning master), becoming the first Roman emperor to match his name (for this reason, he referred to the highest rulers of the Roman Empire before Diocletian as the Chancellor, and Diocletian and his successors as the Emperor). He transplanted the etiquette of Eastern authoritarian countries into his own court, fully enjoying the emperor's authority, and using the god Jupiter to deify himself. [2]
Previously, between 235 and 284, Rome had a succession of 20 to 25 emperors, averaging only two to three years in power. Between 284 and 298 AD, Diocletian gave people the feeling of following the footsteps of his short-lived predecessors and successors. He constantly provoked wars to defend the empire's territory, causing the common people of the empire to constantly rebel. However, in 298 AD, Diocletian successfully prevented the Germanic people from crossing the Danube and Rhine rivers, preventing them from invading the Roman Empire. He also stopped the Persian Empire from invading Syria and Palestine, and defeated his domestic political enemies, which enabled him to successfully stabilize his throne.

Late life
In 305 AD, at the age of 55, after a long period of illness, Diocletian chose to retire and lived in a palace near the center of power, near the Adriatic Sea in Sorona, where he practiced his greatest interest by growing cabbage. Later, someone asked him to ascend the throne again, but he was firmly rejected. He replied, "When you see the vegetables that I personally planted in Sorona, you will not make such a request again.". He was the only Roman emperor who voluntarily relinquished his throne and power; All other emperors either died naturally or were removed by humans.
The "four emperors co governance" designed by Diocletian clearly did not resolve the disputes of the empire. While he was still in power, he could still rely on his own influence to control the situation; Once abdicated, the Roman Empire quickly fell back into internal turmoil.
According to the system he designed, he and Maximian abdicated simultaneously, and both Galerius and Constantius I were elevated from Caesar to Augustus. At the same time, Galerius chose Severus II and Maximinus as Caesar in the west and east, respectively. However, the Italians did not like Severus II, so they elected Maximian's son Maximius as emperor. Severus II was defeated and killed. Galerius was also powerless in this regard.
On the other hand, Constantius I passed away just one year after ascending the throne, and his son Constantine I was elected emperor by the army in York. And Maximian, who had already abdicated, also returned to join the civil war.
The abdicated Diocletian has lost his power, his past achievements have been forgotten, and he has been accused by the Senate as a criminal. His daughter and wife were first imprisoned in Syria and then killed by Li Xini without any charges.
On May 24, 312, Diocletian died in his palace at the age of 62.
The Diocletian Palace later evolved into the cornerstone of the contemporary city of Split, Croatia.

Absolute monarchy
After Diocletian stabilized his position, he began to reform the Roman Empire because he believed that after experiencing a period of internal instability lasting for fifty years, the Roman Empire was on the brink of collapse and could not sustain itself. It began a series of reforms to prevent the empire from falling back into anarchy and maintain its life. This includes dividing the empire in half for easier management, establishing a new system of succession to the throne, strengthening centralization, and completely stripping away the appearance of the Roman Republic (previously known as the Roman Empire but without its name), and making economic reforms to address the extreme inflation that occurred at that time. The Roman Empire has always practiced military dictatorship, but on the surface it was a constitutional monarchy. This constrained its legitimacy by numerous complex titles and conventions, weakening the emperor's control over the legion and the Imperial Guard. This can be seen from the emperor's title as the Supreme Commander, and the emperor's title is also derived from it. These titles, although clumsy, were inherited by numerous Roman emperors in the first two centuries AD. However, starting from Karakara taking over the throne, rulers began to abolish or simplify numerous republic titles and legal systems, and strengthened centralization, making constitutional monarchy virtually non-existent. And these programs left over by the republic also secretly undermine the foundation and legitimacy of the government. Diocletian believed that the title of emperor should be more comprehensive, rather than solely based on military power, and should be more recognizable and stable. So it seeks to establish new regulations, reconfirm the legitimacy of the throne, and depict the emperor as the incarnation of half gods and half humans, as well as the highest priest. At this time, the old title of Pontifex Maximus during the Republican era was given a new meaning, becoming the title of emperor and becoming very important.
Diocletian first chose a new title for himself, calling himself Dominus et deus. This is very different from previous Roman emperors, who usually referred to themselves as heads of state or first citizens, with a certain degree of equality and democracy in their names. Diocletian removed all false titles from his title and established himself as the supreme monarch. It no longer appears in front of the common people. If there are visitors, they need to lie down on the ground and not look directly at the emperor, in order to show grandeur. Visitors are only allowed to lightly kiss the bottom of the emperor's robe. As a result, it created a mysterious, theocratic, and authoritarian government.

Co governance of the Four Emperors
Diocletian, based on his experience of continuous wars in the empire during his first nine years of rule, concluded that the empire was too large to be governed by one emperor alone; And it was also difficult for only one person to resist the constant invasion of barbarians from the Rhine River to the Egyptian border. The complete solution is to divide the empire in half and draw a straight line on the map to divide the empire into two parts, east and west. This division did not only exist for a short period of time, but permanently divided the Roman Empire in the future. The issue of succession to the Roman Empire's throne has never been resolved; It lacks a clear method of succession to the throne, which often leads to civil wars. Early emperors tended to adopt the adoption method, which involved adopting a son and allowing him to inherit the throne. The subsequent military emperors did not like the inheritance law and preferred the family inheritance law, which means that the emperor's son would inherit the throne. The Roman Senate believed that it should have the power to elect a new emperor. So there are at least three, and even more, methods of succession to the throne.
In order to solve the problem of succession to the throne and answer who was the new emperor of the eastern and western parts of the empire, Diocletian first established a four emperor co governance system, which means that the eastern and western parts of the empire are ruled by two main emperors respectively, and each is assisted by a deputy emperor. Among the many titles of Roman emperors, Augustus was the most important, so he was awarded to two main emperors, while the two deputy emperors were given the less important title of Caesar. Diocletian intended for the main emperor to be succeeded by the vice emperor upon retirement or death, while the succeeding main emperor appointed a new vice emperor to solve the problem of succession to the throne.
In 292 AD, Diocletian officially implemented this system and appointed himself as the Eastern Emperor and Maximian as the Western Emperor. The emperor's power was officially divided into two parts. The two emperors established new capitals respectively, and no one took Rome as their capital. When the power of the two main emperors over the empire was increased, the power of the Roman Senate was further reduced to only be limited to the former capital city of Rome. In 293, Diocletian and Maximian each designated a Caesar (Galerius and Constantius I Clonus, respectively) and officially appointed him as their successor. However, they are not just heirs, each of the four emperors ruled over a quarter of the empire.

Compared to the chaos within the Roman Empire in the first half century of Diocletian's accession, the four emperor co governance system created by Diocletian was not much superior, because if any emperor had selfish intentions, this system would collapse. As a result, the opportunistic nature of the Roman Empire's throne quickly led to the collapse of the four emperors co governance system, and the empire returned to a situation where only one person proclaimed himself emperor. In 305 AD, Diocletian retired (and his Western Empire partner also announced his retirement), and the two Caesars became the main emperors according to plan. However, when choosing the new Caesar, the army and the Roman Senate intervened and nominated candidates respectively. In 306 AD, Constantine I launched a civil war in the Western Empire and won in 312 AD. He then occupied the Eastern Empire in 324 AD, restoring the empire to unity until its death in 337 AD. However, in 395, the empire split again into two parts, and this time it never returned to unity.

economic reform
Diocletian also carried out economic reforms. In order to curb inflation, he began issuing new high-purity gold coins, silver coins, and other auxiliary coins. However, the proportion of new coins in the total circulation of currency in the entire empire was too low, coupled with the expulsion of good coins by bad coins and the paralysis of the empire's production, transportation, and sales system, Diocletian's efforts to save currency failed.
In this situation, in 301 AD, Diocletian established the Restriction of Maximum Prices Act (301 Price Edict). This law that limits prices to fixed positions applies to thousands of goods and wages, and imposes the death penalty on violators. However, its official prices were far lower than the cost of products and services, unable to stop inflation from worsening and ultimately overlooked by people. However, it was an important document for understanding the ancient Roman economy.
With the failure of price control, Dai Keli had to rely on a rationing system, completely isolating the supply of military and government supplies from the market, and ensuring the needs of the military and government through the collection of physical taxes, leaving ordinary people to fend for themselves in inflation. [3]
military streamline
Dai Keli first increased the army from 400000 to over 450000 and divided it into two main parts: the border defense army and the reserve field army. About two-thirds of the army is border troops. And the others were field armies, directly controlled by Augustus and Caesar within their territory. Because it is closer to the core of power and more likely to launch a coup, the treatment of the field army is higher than that of the border defense army. This caused resentment among the border troops and plunged the empire into crisis later on.

Based on past experience and the system of the mobile cavalry battalion, Dai Keli first reduced the number of legions in the field army to 1000 per legion, allowing the army to ensure strategic and tactical flexibility without the need to dispatch units for combat. The border army maintains its full strength (4000-6000 personnel). The number of auxiliary troops in each team of the two armies is the same, at 1000 people per team.
During the reign of Diocletian, the power of the command of the Imperial Guard was greatly weakened. Instead, each Augustus and Caesar had two army commanders: the infantry commander and the cavalry commander. This is not only to disperse the military responsibilities of the military commander, but also to reduce the possibility of launching a coup, but it also greatly increased the importance of cavalry in the Roman army.
Many military reforms initiated by Diocletian were continued by his successors and were largely completed by Constantine I. Constantine I abolished the system of the Imperial Guard and replaced it with a finer and easier to control 4000 member Imperial Guard.
Persecute the church
In 303 AD, the Roman Empire launched its final and largest persecution of Christians. In the early period of Diocletian's rule, Galerius was the main instigator of his persecution of Christians, and Diocletian was not particularly eager to persecute Christians. However, in the later period of Diocletian's rule, Diocletian became a monarch who was enthusiastic about persecuting Christians, and on February 24, 303, he issued the first law to persecute Christians.
Firstly, Christian soldiers need to leave the army, and then the private property of the Christian church is confiscated, and Christian books are burned. After being set on fire twice in Diocletian's palace, he took stronger measures against Christians: Christians either gave up their faith or were executed.
This persecution of Christians continued until Constantine I issued the Edict of Milan in 313. Martyrs include Pope Marcelinus, Virgin Philomona, Saint Alfa, Saint Lucia, Saint Elmo, Saint Floriano, Saint George, and Saint Agnes, with the last martyr being Peter of Alexandria (311 AD). This persecution led the church in the Diocese of Alexandria to view the year of Diocletian's accession (284 AD) as a new era of martyrdom. Another influence that persecuted Christians was Marius fleeing to Mount Titano and establishing San Marino there.