The life and death of Jesus, the acts of the apostles.
The beginning of Christianity was in Israel at Pentecost when the Holy Spirit came on the disciples to form the Catholic Church.
I think defined not redefined, because that was just the beginning of Christianity so Paul was defining what Christianity is.
the Bible
Christianity is often considered as beginning at Pentecost, most likely in 33 AD.
It is important in history today because there were many happenings there. All the Crusades were to capture Jerusalem back from the Muslims and to spread Christianity.
A happening is a performance, event or situation meant to be considered as art. Happenings take place anywhere, are often multi-disciplinary, often lack a narrative and frequently seek to involve the audience in some way. Key elements of happenings are planned, but artists sometimes retain room for improvisation. (Wikipedia)
Check out the book of Acts in the Bible.
In most text editors you canmove to the beginning of a line with "Home" key, and to the beginning of the whole text with "Ctrl+Home" key combination.
The Holy Bible.
Jesus is Lord
A summary is the brief happenings of the beginning, middle, and end. It is only the main points. A plot is a what happened in the beginning, middle, and end, with not only the main points, but the character's thoughts and settings of the story.
Well, if you mean the start within the beliefs then the answer is in the beginning of time, if you mean the separation between Judaism and Christianity then the birth of Jesus in Bethlehem and the belief of him being the Messiah, if you mean the beginning of the followers this would be in Israel.