For one thing, Romanticism took from the Neoclassical attitude of seriousness adopted after the Revolution. A further backlash against the licentious lewdness of the Rococo Period, Romanticism (as we mean it here) was a style of art that portrayed dramatic and exotic subjects perceived with strong feelings. This heightened sense of emotion is one of the key differences in Romantic art. Neoclassical paintings like Ingres' Apotheosis of Homer was painted flatly and linearly, you will recall, with not a whole lot of bursting emotion. Romantic paintings breathe emotion. They also shift their focus primarily onto the present, instead of looking back to the Classical past (again, as Ingres' Apotheosis painting did). These paintings often deal with current events but portray them in the fashion one would portray an ancient, epic event of Classical Greek or Roman mythology—dramatically. Romanticism sees all of contemporary life through the Classical lens of epic drama and passionate emotionalism. The changes can be heard in music at this time as easily as the difference between Mozart and Beethoven.
In one sense, then, the court paintings of Jacques-Louis David could be considered Romantic—and they very often are. I placed them under the Neoclassical Period of art because: (1) that is how I was taught; and (2) it helps one to better see the immediate withdrawal away from the Rococo style after the French Revolution. But it is true that David's paintings of Napoleon are as much Romantically inspired as they are Neoclassically styled. His paintings were of contemporary events, like the emperor's coronation; and they were often shown in dramatic fashion, like his painting of Napoleon Crossing the Alps. Romanticism and Neoclassicism share much in common, so I will pick up where we left off and return to another David painting, now under the category of Romantic art.
Just after Napoleon's Syrian Campaign, his troops won a decisive victory over the Ottoman Turks at Jaffa in Israel. After the conquest, many of Napoleon's men were infected with Bubonic plague and deemed incurable. Their emperor had them poisoned to prevent further spread of the disease, but in so doing he fell into disfavor with many among the general public (understandably so, I think). To counter the negative sentiment towards his name, Napoleon turned once more to his favorite painter in order to generate some more promotional propaganda. This time, we see Napoleon at a "pest house" (or plague colony) of infected Bubonic plague victims. The highly contagious nature of the disease made it necessary to isolate those suffering from it to prevent further contamination. It would have been considered absolutely dangerous to enter into a plague house such as we see here, but Napoleon stands upright and calm. It would have been considered even more dangerous not to have a cloth or handkerchief covering one's mouth while among the colony. It would have been considered complete suicide to touch one of the sick, but Napoleon, with no glove or cloth to protect him, stretches out his helping hand like the great Healer, Christ Himself. Meanwhile we can see the city of Jaffa burning in the background with a French flag staked over it, but this is conveniently pushed away from the scene at present. What artist Jacques-Louis David has painted is an extraordinary image of Napoleon as a fearless general, a compassionate leader, a helper of the weak, and an inspiration to his men, a great emperor, and no less great a man than the Son of Man. Propaganda makes heroes.