Some antisemitic allegations date back to the birth of Christianity, while some conspiracy theories are more recent. Since at least the Middle Ages, antisemitism has featured elements of conspiracy theory. In medieval Europe it was widely believed that Jews poisoned wells, had been responsible for the death of Jesus, and ritually consumed the blood of Christians. The second half of the 19th century saw the emergence of notions that Jews and/or Freemasons were plotting to establish control over the world. Forged evidence has been presented to spread the notion that Jews were responsible for the propagation of Communism, the most notorious example being The Protocols of the Elders of Zion (1903). Such antisemitic conspiracy theories became central to the worldview of Adolf Hitler. Antisemitic theories persist today in notions concerning banking, Hollywood, the news media and a purported Zionist Occupation Government.
Holocaust denial is also considered an antisemitic conspiracy theory because of its position that the Holocaust is a hoax designed to advance the interests of Jews and justify the creation of the State of Israel.
The blame for the death of Jesus has often been cast toward the Jews. The Gospel accounts of Matthew, Mark, Luke and John all contain the betrayal of Jesus by his disciple, Judas Iscariot, into the hands of the ruling religious Jews (see Sanhedrin Trial of Jesus). According to the New Testament accounts, the Jewish authorities in Judea charged Jesus with blasphemy and sought his execution. However, the Jewish authorities in this case seem to have lacked the authority to have Jesus put to death, according to John 18:31. They brought Jesus to Pontius Pilate, the Roman Governor of Iudaea Province, who consented to Jesus' execution.
Pilate is portrayed in the Gospel accounts as a reluctant accomplice to Jesus' death. All four Gospels indicate that there may have been hesitation on the part of both Jewish and Roman authorities to act immediately or needlessly in the face of potential popular opposition (Matt 26:4–5; Mk 15:12–15; Lk 22:1–2). The four Gospel accounts also all portray the Roman Governor Pilate as partly responsible for Jesus' execution, and never claim he is without guilt (though his attempt at self-exoneration is mentioned).
According to the Epistle to the Romans, Jesus' death was necessary to save humanity; the author of Hebrews calls out all backsliding Christians for "crucifying the Son of God all over again". Paul the Apostle, in 1 Thessalonians, noted that the same Jews who had Jesus crucified continued in their persecution of the church. This passage was frequently used to assign guilt for Christ's death specifically to Jewish people everywhere and throughout all generations. As a part of Second Vatican Council, the Roman Catholic Church under Pope Paul VI issued the document Nostra aetate, repudiating the idea of collective Jewish guilt for the Crucifixion.