Was Christianity an Invention of the Fourth Century?

     There is a pernicious idea out there now, that has gained traction far beyond what it is worth, that Christianity and even the Holy Scriptures were originally invented by Constantine and the Ecumenical Councils in the fourth century. The truth, like with most things of ancient origin, is far more complex than this. Was Christianity a product of the machinations of a fourth century Roman emperor?
     The answer is both a definitive "no"... and a qualified "yes."
     I will address the qualified "yes" first. What we know as Christianity today, that is, "modern" Christianity very much has its origins in Constantine and the Church Councils. It was those Councils  that gave us the codified doctrines of the hypostatic union of Christ, the doctrine of the Holy Trinity, the one among many lists of books and documents accepted as Holy Scripture, the Nicene Creed which forms the standard of orthodox belief, and so on. All of these things form the bedrock of all modern Christian churches and denominations to one extant or another as well as the inherited bias and need to eliminate any teaching or doctrine that deviates from that which was canonized at the Councils for one reason or another. One can either assume that the Councils and Constantine could do no wrong and were each one a Saint, or one can demonize them up one side and down the other. However, the fact remains that virtually all Christian churches from Eastern Orthodox to Roman Catholic, from Baptist to Evangelical, and from Presbyterian to Pentecostal to Anglican trace their lineage back to Constantine's desire to unite the seemingly fragmented Christians into a cohesive whole, and the seven Ecumenical Councils starting with Nicea.
      But the answer is also a definitive "NO." What Constantine shaped into the "One Holy Catholic and Apostolic Church" was originally something that looked very different from the grand spectacles of the organized Church, but it very much existed prior to the fourth century. We know this because of all of the writings which those early Christians left behind, both as what became the New Testament, written in the first century, but also what are known as the writings of the "ante-Nicene Fathers," that is, those Christian leaders and thinkers that lived between the first and fourth centuries.
     How do we know that these writings were written when they were supposed to be written? And by whom? We know this from the dialects of the languages in which they were written, both Koine Greek (the majority) and pre-Ecclesiastical Latin. We know that each of these documents clearly had their own author with their own use of syntax, vocabulary, and style which is like a fingerprint to an author (It is frequently how authors today can be identified even if they're writing under a pseudonym). And we know that the language used fits the time period in which they were purported to have been written. What do I mean by this? Eighteenth century British English is worded differently from twenty-first century American English. One only has to peruse Jane Austin or Charlotte Bronte to understand that we do not speak like they did almost three hundred years ago. The differences grow greater the farther the distance in time, as anyone who compares Shakespeare and Beowulf to modern English will attest. Fourth century Byzantine Greek cannot be mistaken for first century or even second century Koine. And had someone attempted to do so, it would have come off as "wonky," anachronistic, and just "not right," compare the King James Version of the Bible (1611) with the Book of Mormon (1830-40) and you'll see what I mean. Those who make such claims about the late or even pseudo-authorship of the Holy Scriptures or the Early Church Fathers do so from a position of ignorance about the language of the original texts, not being able to read and compare them, or not bothering to.
     The earliest Christians only wrote and taught what they had seen and heard happen. The documents of the New Testament, all of which demonstrate socio-linguistic authenticity to the period, attest to this. When they wrote about Jesus rising from the dead, it was because that was what happened, and every one of them went to their executions (except John, but not for lack of trying) refusing to recant what they had personally seen. They taught what Jesus Himself had taught them, and those after them attempted to do the same. No more, and no less. Yes, they wrote about the miracles Jesus did, as well as being able to perform similar things to Him. What's really interesting about this in the later writings, those of the second and third centuries, is that they write about them to non-Christians under the assumption that, not only did these non-Christians know what they were talking about, but could verify what they said through their own experiences. They also talk plainly about these demonstrations beginning to grow rarer towards the end of the third century and into the fourth.
     The earliest Christians focused heavily, not on theological doctrines of what someone had to believe about things they couldn't verify or see, but on how a Christian was to live their lives. For them, a Christian was only a Christian if their behavior matched that of Jesus Christ. If they "walked as He walked." And this was true regardless of what theological speculation they spouted. There were a great many speculations and disagreements about the nature of God, Christ, their relationship, and so on in these writings, but they nearly always agreed on this central point, that in order for a Christian to be a Christian, he had to demonstrate it by acting like Jesus.
     This was something Constantine, being a pagan Roman, didn't understand. He only saw the chaos of speculations, and not the common unified understanding. Unfortunately, too many bishops and pastors of the churches were too caught up in these disagreements as well by this point, and they jumped at the chance to have official, if managed, recognition within the empire. Yet, prior to and even afterwards, both heretics and "orthodox" were tortured, executed, and martyred because of their adherence to Jesus Christ and what He taught. Unfortunately Constantine's reasonably understandable, even commendable efforts to bring order to his empire by bringing order to the "chaos" of Christianity, something he didn't really understand, missed the point entirely.