Erastus - see the notes on Romans 16:23.
Abode at Corinth - This was his home, where he filled an important office; see the notes at Romans 16:23. It would seem that when Paul went to Rome, there was some expectation that he would accompany him, but that reasons had occurred for his remaining in Corinth. His doing so is referred to without blame.
But Trophimus - see Acts 20:4. He was a native of Asia Minor.
Have I left at Miletum sick - Probably he designed to accompany him to Rome, as he had been often with him in his journeys. On the situation of Miletus, or Miletum, see the notes on Acts 20:15.