There are actually two versions of this painting in Rome, one at the Vatican and one at the collection of the Dora Pamphilij. Caravaggio painted around eight of St John the Baptist altogether, making it his most prolific set of works on one subject. They are sometimes referred to as ‘Youth with Ram’, since the Saint is always depicted with a ram. The Capitoline work carries over many of the concerns which animated Caravaggio's other work from this period. The leaves behind the figure, and the plants and soil around his feet, are depicted with that careful, almost photographic sense of detail which is seen in the contemporary still life Basket of Fruit, while the melancholy self-absorption of the Baptist creates an atmosphere of introspection. The grape leaves stand for the grapes from which the wine of the Last Supper was pressed, while the thorns call to mind the Crown of Thorns, and the sheep is a reminder of the Sacrifice of Christ. The pose adopted by the model is a clear imitation of that adopted by one of Michelangelo's famous ignudi on the ceiling of the Sistine Chapel (1508-1512). The role of these enormous male nudes in Michelango's depiction of the world before the Laws of Moses has always been unclear – some have supposed them to be angels, others that they represent the Neo-Platonic ideal of human beauty – but for Caravaggio to pose his adolescent assistant as one of the Master's dignified witnesses to the Creation was clearly a kind of in-joke for the cognoscenti.

The Doria Pamphilj version is a copy of the original in the Vatican, completed by Caravaggio because the original was so popular. It has deeper contrasts than the Vatican version, possibly due to the original being restored at some earlier time. I think the deeper chiaroscuro actually improves upon it.