I thought that I had blogged about this, but it seems I did not, or at least, can’t find it if I did.
The ancient festival of the Lupercalia was only abolished late in the 5th century. Pope Gelasius wrote a letter to the senator Andromachus, justifying the move. It’s found in the Collectio Avellana, which was published as CSEL 35.1 and 35.2 a century ago, as letter 100. The letter is on p.453-464 of vol. 1, which is p.566-577 of the PDF.
I think that would be an interesting letter to have online. I’ve put out an enquiry in StudentGems to see if I can find someone to translate it.
UPDATE: I did.