Ulysses is standing aloft on his ship deriding the Cyclops, whom he and his companions have just left blinded, and invoking the vengeance of Neptune. One of the flags is painted with the scene of the Trojan Horse. The horses of the Sun are rising above the horizon ('Odyssey', Book 9).
Apparently the idea was in Turner's mind as early as about 1807, if this is the correct date of a sketchbook which contains a rough drawing of the subject. The picture was exhibited at the Royal Academy in 1829.