This scene comes from the twelve-part tapestry series on the history of the Roman emperor Constantine that Rubens designed for King Louis XIII of France. In October AD 312, Constantine defeated his coregent Maxentius at the Battle of the Milvian Bridge.
In Rubens’s time and up into the twentieth century, Constantine was considered the first Christian emperor. He was therefore a highly suitable exemplar to be used in praise of the ‘most Christian king’ (rex christianissimus) of France.