Adam Clarke on 2 Corinthians 11:25

Thrice was I beaten with rods - This was under the Roman government, as their lictors beat criminals in this way. We hear of the apostle's being treated thus once, namely at Philippi, Act 16:22. See Section 9 of the Introduction.

Once was I stoned - Namely, at Lystra, Act 14:19, etc.

A night and a day I have been in the deep - To what this refers we cannot tell; it is generally supposed that in some shipwreck not on record the apostle had saved himself on a plank, and was a whole day and night on the sea, tossed about at the mercy of the waves. Others think that βυθος, the deep, signifies a dungeon of a terrible nature at Cyzicum, in the Propontis, into which Paul was cast as he passed from Troas. But this is not likely.