Leonardo da Vinci calculated the gravitational constant almost exactly long before Newton.

Modern physicists have discovered a series of sketches in da Vinci's diaries with triangles and sand-like particles pouring out of a jar. They translated notes written in the famous left-handed mirror script, which reads from right to left. It turned out that da Vinci described experiments with the fall of various objects. He already then suggested that water or sand would not fall at a constant speed, but would rather accelerate due to gravity - this idea was far ahead of its time.