Answer: well because 4 black bulls and specific one that is 17 feet long.
Explanation: "The Hall of Bulls is painting on the wall that shows 4 bulls that are black colored and very big. One of the bulls is 17 feet long and that specific about this painting and it made it so famous and memorable. Those paintings on the walls are founded in deep underground painted by people of Old Stone Age in France, Lascaux. There was a lot of painting on the walls in caves which are showing animals such as cows, horses, and bison and geometric images. Painting 'The Hall of Bulls' is the most famous one. "