In hoc signo vinces. As described by Eusebius, a 4th century chronicler, this inscription and sign of the cross supposedly appeared to Emperor Constantine the Great before the Battle of Rome with his political opponent Maccensius in 312. The battle took place at the Mulvian Bridge. Constantine defeated Maccensius' more numerous hosts and entered Rome. In 313 Constantine (the first Roman emperor to become a Christian) introduced an act of religious tolerance called the Edict of Milan, which put an end to the persecution of Christians, who after the crucifixion of Jesus were being mass-murdered and persecuted by their religious opponents, whether Roman or Jewish, or by any pagan peoples. Rome was taking Christianity under its protection.
It is true that subsequent emperors withdrew from this protection and the persecution of Christians increased, but despite this, Christianity spread throughout the Roman Empire and became the universal Roman religion, i.e. Catholicism.
Finally, Emperor Theodosius the Great, who ruled both the eastern and western parts of the Roman Empire, put the final straw by establishing Christianity as the universal religion of the Roman Empire, as the binding religion. From now on, previous persecutors had to grace Christians, pretend to be friends, because if not, you could lose a lot, because the Roman emperors did not care about the opinion of the Helsinki Organization for Human Rights.
Therefore, at the end of the fourth century, and even more so from the fifth century, Christianity and the Roman Empire played on the same team, and Rome became both the capital and the symbol of both the power of the Roman Emperor and the Pope - the leader of Christians. As a result, the role of the pope was sometimes respected more than that of the emperor, after all, it was as a result of talks not with the emperor but with Pope Leo I in 452 that the armies of Attila, attacking the Empire - solely out of respect for the papal majesty - abandoned the destruction of Rome. And it was gradually the Pope, rather than the Emperor, who was seen as the spiritual leader of the Empire.
In 476 the Empire collapsed as a unified state organization, but not as an idea, not as Rome; Rome continued to exist as the very concept and symbol of world power. And Rome had a pope, and he was associated as the ruler of the empire, admittedly without an army, but armies were still somewhere in the provinces, as before, but there needed to be a commander in chief, a point of reference, whether it was Caesar or Augustus or whoever, whatever, there was always someone at the top of the empire. When the emperor was absent, this role fell, as it were, inherently to the pope.
In Frankish territory, Christianity was declared to be defended by Chlodwig, one of the first rulers of the Merovingian dynasty, who was baptized in 496, and thus the center of gravity of the military power of the Roman empire shifted to the land of the Franks, and the Merovingians became its possessors. The Merovingians acquired vast territories and established a powerful kingdom, but after Dagobert's death in 639, the successive rulers and their courtiers concentrated on organizing court intrigues and elaborate orgies (they later became known in history as the "dull kings"), handing over the day-to-day business of running the country to their majordomuses.
Meanwhile, from the 7th century on, a new global player emerged: the Islamic Empire, which by the 8th century had already conquered the entire Iberian Peninsula and was encroaching on Frankish territory.
The Merovingian rulers of France, busy organizing their parties, were unable to resist the mighty Islam, and Frankish territory crumbled under the onslaught of the Islamic army. It was not until their majordomo Charles the Hammer, commanding the army of the Franks, put up an armed resistance to the Saracens. He won the Battle of Poitiers, defeated and repelled the Islamists, and then his sons kicked the Merovingians out of their royal seats, and themselves took the royal crown and created the Carolingian royal dynasty.
Resisting the mighty Islam, the Frankish territory crumbled under the onslaught of the Islamic armies. It was not until their majordomo Charles the Hammer, commanding the army of the Franks, put up an armed resistance to the Saracens. He won the Battle of Poitiers, defeated and repulsed the Islamists and then his sons kicked the Merovingians out of their royal seats, and themselves took the royal crown and created the Carolingian royal dynasty.
The suppression of Islam by the Carolingians, (suppression because the defeat of Islam was only achieved by the victory of King Sobieski at Vienna) results in the restoration of the title of Roman Emperor to the Frankish leader Charlemagne in 800.
The next titles of emperors were given to kings of the Franks or Italy, but after the assassination of emperor Berenger in 924, there was a long period, 38 years, when the title was not given.
Finally, in 962, the title fell to the king of the Germans from the Ludolfing family. The Germans could not enlarge the territory of the empire in the west, because there was already Christianity there and they needed some other reason for war. But the eastern territories, where Christianity had not yet been introduced, were another matter. They can be freely attacked and plundered without special thought or reason, under the pretext of fighting for peace, democracy ... no, it is too early... then it was about Christianity. As it were, the political concept of Drang nach Osten is automatically born.
At that time it so happens that the ruler of Poland, the lands bordering the empire directly from the east, is Mieszko I of the Piast dynasty, who turns out to be a master of war and diplomacy.
It was the concept of Drang nach Osten that led to written reports about those times and Mieszko's state (various wise men born hundreds of years later will interpret those reports in different ways). Thus the 10th century Saxon chronicler Vidukindus Corbeius describes Wichman's expedition to the east: the king of Mieszko, whose authority was subordinated to the Slavs, called Licikaviki, he defeated twice, killed his brother, and squeezed out a great booty from him. Interesting is here the use of the name Licikaviki, according to some researchers a distorted name Lechici, which would suggest that the word Lachy used for the Poles and in much later times has its roots in the name of Mieszko I's grandfather - Lestek. Probably Lestek's state was much smaller than those at the time of Mieszko, probably the tribal roots come from the lands of Wielkopolska in the region of Gniezno, Giecz, Poznan or Kalisz. However, when describing the life of St. Adalbert, St. Bruno of Kwerfurt (a chronicler and missionary from the 10th / 11th century) uses the name Polans, which is explained by Jan Długosz as follows: "The Lechites, those in particular who sat in the fields, were called Polans by other tribes related to them, nomadic in the forests, i.e. the inhabitants of the fields, and this tribe was called Polan. This name later became so popular among people that the old name (Lechitas) was forgotten and the nation and the whole country started to be called Poland".
Mieszko's military attention was focused on the direction of the threat, that is, on the western borders of Poland. German margraves tried to "pluck" Mieszko's country, which was a pagan country. However, after his marriage in 965 with a Bohemian princess from a Christian country, and after his baptism in 966 (but the baptism came from Bohemia, not from the German emperor), Mieszko became a "friend of the emperor", an independent ruler of a Christian country, and German margraves, who would not respect that fact, were able to eliminate his intention to push eastwards, which he proves in the battle of Cedynia in 972 (in which Mieszko's brother Czcibor was especially meritorious). It is said that only a handful of Germans escaped from that battle, which worried Emperor Otto to such an extent that he demanded that his son Mieszko (later King Boleslaw the Brave) be betrayed, so that Mieszko would not think of making a Drang nach Westen.
Later Mieszko tried to maintain good relations with the emperor (after all his son was a hostage), but it is clear that he did not trust German emperors and at the end of his life he handed over the Polish state to the direct care of the Papacy, which is stated in the document Dagome iudex. From now on Poland is linked to Rome not only on a religious but also on a political basis. Submission of Poland to the direct authority of the Papacy put Poland in a legal and administrative position almost equal to that of the empire because the emperor was also appointed by the Pope. The direct submission of Poland to the Papacy as if removed Poland from direct subjection to the Empire, because Poland is a direct subject of the Papacy - like the Emperor, and being under the direct authority of the same master they are in a way equal to each other.
Baptism from Bohemia rather than Germany and the submission of Poland to the Papacy was a political masterstroke by Mieszko I.
This move was also important for the coronation act of Mieszko's successors. For it was important from whom the crown was given. The emperor came to the Gniezno convention in 1000 and crowned Chrobry with his crown, but Chrobry asked for a "papal" coronation and finally the coronation act was performed by a papal representative in 1025.
Was the adoption of Christianity merely a political act by Mieszko? Such a change of party affiliation just to stay afloat? A manoeuvre popular in the games of contemporary political parties?
The spreading of a new idea and especially a new religion provokes resistance and hostile actions of the followers of the old religion, especially its priests, who derive from it not only income, but also a distinguished social position. Description of the murder of St. Adalbert during his missionary expedition to the Prusai land, when the group of killers was led by a local priest (and also according to some chronicles, he himself stabbed a spear in the heart of St. Adalbert) shows how before the new religion defended their interests primarily pagan priests - killing the missionaries. We can say that this is a typical example of the behavior of all pagan priests, where religious power was closely related to political power and where, therefore, the loss of religious power meant the loss of political power. After all, this example occurred from the very beginning of the rise of Christianity.
Although missionaries were murdered on their way to neighboring lands such as Prussia, no missionaries were murdered on the territory ruled by Mieszko I. This suggests that Christianity did not meet with much resistance among the people of Lechit, as Widukindus wants, or Polan, as Bruno wants. Whether this was due to the authority of Mieszko and his son Boleslaw Chrobry or to universal Christian values or something else is difficult to say.
It cannot be ruled out that Christianity was known among the Piast people even before it was officially adopted, after all, trade routes from the Roman Empire or the later empire of Charlemagne led through those territories, and it could not have happened without the transmission of news from distant lands.
The attitude to a new religion is certainly influenced by the beliefs that prevailed among a given community. There are various theories about the beliefs of different Slavs, but they mainly concern the Slavs of the Polabian region or the Slavs east of the Vistula. However, there is no information about the religion of the tribes living between the Oder and Vistula Lechit or Polan, as if they had no religion beyond a natural belief that there is good and evil in the environment of folk folklore, which could be one of the reasons that there was no special resistance to Christianity and listening to missionaries. And perhaps Christianity was the first systematized and compact religion for the Polans in general.
Moreover, there is much to suggest that in Piast times Polish society, apart from the person of the ruler himself, his closest associates and his personal team, was a one-class society with no distinguished privileged strata. After all, a similar organization could be found among the tribes living to the northeast of the Poles - the Prussians or Warmians, who did not have any division into social classes and only for the period of wars chose a commander-king. One may wonder whether this social structure, after all compatible with the main principles of the New Covenant preached by the missionaries of that time (the Bible with the attached Old Testament was the obligatory "religious textbook" in Poland as late as 1564), was not one of the reasons for the attractiveness and rapid absorption of Christianity in Poland, for which Mieszko I opened the doors.
Be that as it may, Christianity with its system of values came together in one act with the creation of a state system, one organizational act creating a state, a religion and an international political arrangement excluding Poland, at least in a legal sense, from dependence on the empire.
Mieszko I, although his son received the royal crown from the Pope, was more than just a king for Poland; he was the founding father of a state - Catholic Poland.
(Translated with www.DeepL.com/Translator)