In 2 Corinthians 11:16, Paul begins his “foolish boasting.” Rather than giving the Corinthians a summary of impressive accomplishments to prove his legitimacy as an apostle, he launches into a list of his struggles and humiliations. At the very end of chapter 11, he includes this final boast, highlighted by a longer introduction:
If boasting is the name of the game, then I’m going to boast of things to do with my weakness.
The God and Father of the Lord Jesus knows, blessed be he for ever, that I am not lying: [once], at Damascus, the governor of King Aretas was guarding the city of the Damascenes, to arrest me, and I was let down through a window in the wall in a basket, and escaped his hands! — Fr. Nicholas King Translation
It sounds like Paul is taking a formal oath, calling God as his witness for something. Why would he stop the flow of his long list of hardships to call God as his witness for this event? N. T. Wright provides a bit of historical background in The Resurrection of the Son of God, page 308: one of the highest Roman military honors was the Corona Murialis — the walled crown. It was bestowed on the first soldier who successfully climbed over the wall of a city during a siege. The award recipient would swear an oath to claim his prize.
Paul parodies this high honor to poke fun at himself. He solemnly swears that he was the first one over the wall at Damascus — in retreat!