Last year my wife and I went on a tour of Turkey. While we were there we visited the ancient Roman city Aphrodisias where I was first introduced to a former slave named Zoilos. I posted a blog about our visit (here) with some thoughts on the similarities and differences between Zoilos and Onesimus.
Last month I published an article in Biblical Archaeology Review based on that blog post. An edited version is now available on Bible History Daily.
Incidentally, my friend and colleague, Tim Gombis, is beginning a series on Philemon & Onesimus over on his blog Faith Improvised. Tim is going to argue that Philemon and Onesimus were actual brothers. Tim and I have talked about this in private and he knows that I disagree with him. But I look forward to hearing his thoughts afresh now that he has had time to put them in the form of a research paper. Perhaps he will change my mind.