I'm in an undergraduate course on the Reformation and we are currently in the middle of reading Erasmus' The Praise of Folly which I've so far found super interesting and fun to read. However, in the introduction, there were several mentions of the "Pauline Folly of the Cross". What did this term refer to in 15th and 16th century Europe?
I'm not a historian as such, but did some history courses at university, and did study The Praise of Folly at one point. But this answer is coming from my christian knowledge of the letters written by Paul.
I can say that "Pauline Folly of the Cross" is referring to Paul's thinking about the message of Christ being crucified, which was a message that seemed foolish to many of his hearers. His thinking was that when we see Christ being executed in a very gross way it does not in any way seem to be a victory, it seems vile and not a thing you'd want to think about much. The idea that it could provide salvation seems very foolish (from our natural point of view). Yet Paul as well as the apostles believed it did, and preached it. Paul often preached in Greek cities and Greek intellectuals loved great logic and displays of the intellect, so the salvation through the cross message seemed foolish and illogical to many hearers (he did not do very well in ultra-philosophical Athens, but fared better in Corinth, having rethought his approach, he was trying to argue as a philosopher in Athens).
Paul in his first letter to the Corinthians says the message of the Cross is foolishness to many Greeks (it seemed foolish, that is), hence not many of the christian believers in Corinth were "wise according to worldly standards, not many were powerful, not many were of noble birth" (1 Corinthians 1:26).
1 Corinthians 1:20-25 "Where is the one who is wise? Where is the scribe? Where is the debater of this age? Has not God made foolish the wisdom of this world? for since, in the wisdom of God, the world did not know God through wisdom, it pleased God through the folly of what we preach to save those who believe. For Jews demand signs and Greeks seek wisdom, but we preach Christ crucified, a stumbling block to Jews and folly to Gentiles, but to those who are called, both Jews and Greeks, Christ is the power of God and the wisdom of God. For the foolishness of God [my aside: it's not really foolishness, but often gets viewed as foolish] is wiser than men, and the weakness of God is stronger than men."
(Paul arrives in Athens in Acts 17:16-34, and in Corinth in Acts 18:1-18, where he stayed for 1.5 years.)