Focus on Conversion on the Way to Damascus and explain the Style.
IconographyWell-established iconographic tradition stipulated how the Conversion of Paul should be depicted in Renaissance and Baroque art. Its characteristic elements were a rearing, panicked horse—although there is no mention of a horse in the Bible—with Saul lying on the ground, Jesus appearing in the sky and a retinue of soldiers reacting to the events. This is how Taddeo Zuccari, one of the most renowned painters in Caravaggio's Rome, portrayed the scene on a large altarpiece in the Church of San Marcello al Corso around 1560. The figure of Paul in the Cerasi Conversion was derived from a model by Raphael via Zuccari. Raphael's version was part of his series of tapestries created for the Sistine Chapel in 1515–16.
"If we could turn Raphael's Saint Paul in such a way that his head would touch the lower frame and the length of his body would be directed more or less orthogonally inward, we would have a figure similar to that in Caravaggio's painting", observed Walter Friedlaender. He also suggested that the inspiration for the horse was Albrecht Dürer's most famous print, The Large Horse (1505), whose main subject has the same bulky, powerful hindquarters and the rest of its body is seen from a similar oblique angle.Another possible source for the painting is a four-block woodcut attributed to Ugo da Carpi (c. 1515–20) whose central detail depicts Saul on the ground and a groom trying to calm his panicked horse and leading the animal away. This is the only known example among the antecedents which represents exactly the same moment as Caravaggio's painting. A more obvious, although less close precursor was the Conversion of Saint Paul by Michelangelo in the Pauline Chapel (1542–45) where a rearing horse and a soldier holding its bridle are conspicuous elements in the middle of the crowded scene. A painting that Caravaggio must have known was a very unusual Conversion which Moretto da Brescia painted for the Mint of Milan in 1540–41. This scene consists only two figures: Saul and his horse, and the horse strangely dominates the painting. Moretto was probably inspired by a similar Conversion attributed to Parmigianino (1527). 
Although some details and motifs may have been borrowed or inspired by these artworks, it is important to note that the pared-down composition and the intense spiritual drama of the Cerasi Conversion was a novelty without any direct iconographic precedent at the time. It represented a break with the tradition that even Caravaggio's own previous version more or less followed.
TenebrismMost of Caravaggio's paintings after 1600 depicted religious subjects, and were placed in churches. According to Denis Mahon, the two paintings in the Cerasi Chapel form "a closely-knit group of sufficiently clear character" with The Inspiration of Saint Matthew in the Contarelli Chapel and The Entombment of Christ in the Pinacoteca Vaticana. He called these four works "the middle group" and stated that they belong to Caravaggio's mature period. Comparing the two paintings in the Cerasi Chapel, Mahon saw the Conversion of Saint Paul "much more animated than its companion". This is conveyed solely by the ingenious use of the light because Caravaggio eschewed any but the slightest movements. This way he rendered "the scene unclear, mysterious and therefore curiously mouvementé."Caravaggio's style of tenebrism, where forms in paintings emerge from a dark background with usually one source of stark light, created dramatic effects with its strong contrasts. This lighting was evoking spiritual drama in the Conversion of Saint Paul. The brighter areas are juxtaposed with "heavy dark patches, especially deep beneath the horse's belly and extending into impenetrable darkness that lies outside and beyond the circular grouping of the three figures". The usual landscape background was dismissed entirely and replaced with an intense concentration on the three figures who compose the scene. The strong light and the enveloping darkness makes this focus even more intense.
The unusual placement of the characters also served to convey the intensity of the moment. Although Saul gets the most light, the attention is given to him in a strange way. Lying on the ground, he is much smaller than the horse, which is also at the center of the painting. Paul's body is foreshortened, and is not facing the viewer, and yet his presence is the most powerful because of his body is pushing into the viewer's space. The position of the horse and especially the front leg, which is hanging in the air, creates even more visual tension. The first compositional draft revealed by the X-ray examination was a more traditional composition with a visible source of divine radiance coming from the left.
Sistine Chapel Ugo da Carpi Raphael Parmigianino Moretto da Brescia Rome Denis Mahon Pauline Chapel series of tapestries Tenebrism San Marcello al Corso Cerasi Chapel right Walter Friedlaender The Inspiration of Saint Matthew Taddeo Zuccari Pinacoteca Vaticana altarpiece Caravaggio Conversion of Saint Paul Michelangelo tenebrism left Albrecht Dürer Contarelli Chapel