How did 'escape velocity' contribute to the idea of black holes?

The idea of black holes goes back to the 1780s and 1790s. There were two physicists working at the time that had the same idea independently of each other. One was a clergyman called John Michell and the other was the great French mathematician, Pierre-Simon Laplace. And they were both thinking in terms of an idea called 'escape velocity.' The escape velocity is the speed you have to travel to completely escape the gravitational pull of an object. Physicist Brian Cox on how escape velocity lead to the idea of black holes.