The demolition "raven" of Diades. Photo : Augusta Stylianou Artist

It was a tall scaffold on wheels from which a long wooden beam was suspended. The front end of the beam had a metal hook or grab. The operators, with ropes fastened to the rear end of the beam, led the hook to a stone at the top of the enemy wall and once they had grabbed it, they pulled the ropes with force, pulling it down. In this way, the demolished the enemy wall from top to bottom.
Sources
Vitruvius, On Architecture