This is "Kings Clothar and Dagobert dispute with a Herald" painted by Peter Paul Rubens. Created between 1611-12, it's an oil on wood painting that showcases the artist's skill in composition and use of light.
The central panel depicts Saint Bavo being received as a monk, while the right panel shows King Clothar and his son Dagobert sitting astride their horses. The two kings hold out their arms to block a herald from the Roman Emperor Mauritius, who is trying to deliver an edict forbidding soldiers from becoming monks.
Notice how the silvery steed of Dagobert dominates the composition - its body covers almost the entire width of the painting. The richness of the dark blue and silver armour adds depth to the scene. You can see the tension in the situation as the raised hoof of one horse creates a sense of restlessness, while the distressed dog trapped beneath the horse adds to this feeling.
Rubens used quick brushstrokes for most of the composition but applied impasto to intensify the reflection of light on the armour and horses. The background figures are loosely defined, indicating that this was an oil sketch used as a plan for a later painting.
Kings Clothar and Dagobert dispute with a Herald hangs in The National Gallery on Trafalgar Square, London — free to enter. Point your phone at any artwork there and audioguide.london plays a free audio guide in six languages — no app download needed.