Palm Sunday or Passion Sunday is the beginning of the most holy
week of the Christian year. There is no doubt the event of Jesus riding into Jerusalem took place and can be verified by researching the history of the Christian World as written by non-Christians and by Christians.
There is factual info written by men who lived at the time. They are Flavius Josephus a Jew who wrote and published Antiquities of the Jews covering the history of the Jewish people from creation to the reign of the Roman Emperor Nero, Pliny the Younger, Tacitus, a Roman historian, Gaius Tranquillus also a Roman historian—and others.
Book 18 ,chapter 3 of Antiquities confirms the existence of JESUS : “Now there was about this time JESUS, a wise man if it be lawful to call Him a man, for he was a doer of wonderful works---a teacher of such men as received the truth with pleasure.….He drew over to him both Jews and Gentiles---He was the Christ.”
The gospel writers, the Evangelist Luke who wrote the Acts of the Apostles and the Gospel according to Luke, Mark, Mathew and John who also wrote their own gospels all testify to the truth of our Christian heritage and teaching. It is all stored in the archives of the Vatican Library.
Holy Week begins on "Passion (or Palm) Sunday” which speaks of Christ's regal entrance and triumph into Jerusalem, the proclamation of the Passion, Death, Resurrection and the beginning of the Church confirmed by the Resurrection on Easter Sunday which made the sacraments of reconciliation and the Eucharist real.