The French frigate Méduse ran aground off the coast of today’s Mauritania on 2 July 1816. From the c. 147 initial survivors, only 15 were rescued. Those who survived endured starvation, dehydration and practised cannibalism. The painting shows the moment they see a ship in the distance.
The picture doesn’t do justice to the original painting which is a whopping 491 cm × 716 cm (16 ft 1 in × 23 ft 6 in) and can be seen in The Louvre.