The Emperor Theodosius is forbidden by Saint Ambrose to enter Milan Cathedral

The Emperor Theodosius (about 346–395) – the figure in a red cape, laurel wreath and armour – is being blocked from entering Milan Cathedral by the bishop of the city, Saint Ambrose. Theodosius had massacred the people of Thessalonica for their role in the murder of his general, Butheric, so the saint banned him from the cathedral.This encounter is recorded in the Golden Legend, a medieval compilation of saints‘ lives. In this painting, the Emperor is accompanied by three soldiers. One of them, on the far left, wears a haughty expression and holds an arrogant pose; the dog at his feet identifies him as Ruffinus, to whom Saint Ambrose declared: ’Thou hast no more shame than a hound.' The rebuke is intensified by the saint’s gaze, which is focused on Ruffinus rather than Theodosius, who stands immediately in front of him and is the subject of the story. Like the Emperor, Saint Ambrose is surrounded by a group of supporters. The man second from the right, whose face is most clearly detailed and illuminated, has been identified as Nicholaes Rockox, alderman of Antwerp. Rockox commissioned Samson and Delilah from Rubens and may have also commissioned this picture.Van Dyck based his depiction of the story on a version of the same subject by Peter Paul Rubens, dated to around 1615–16 (Kunsthistorisches Museum, Vienna). Van Dyck worked as an assistant in Rubens’s studio around 1618–20, and he drew much influence and inspiration from the older artist. He brought his own imaginative flare to his pictures, however, and there are significant differences between this painting and Rubens’s original. This version is less than half the size of the original, and Van Dyck also made changes to the composition. He extended the architecture, bringing it further forward so that it dominates the background and pushes the figures together, giving the scene a more immediate sense of confrontation. Some of the figures’ facial features have also been altered: in the National Gallery picture, the Emperor and his followers are beardless, unlike in Rubens’s version.Van Dyck made several of these changes while he was painting. He had begun by following Rubens’s original more closely, but altered details as he progressed to infuse the picture with his own distinctive character. Some of these pentimenti can be seen with the naked eye and some can be seen in X-ray and infrared images taken of the painting.