I don't think the phase " The road to hell is paved with the skull of Bishops" is a contemporary one. Perhaps another reader will know the source and post it.
Saint John Chrysostom (347-407) said "The floor of hell is paved with the skulls of Bishops".
http://www.chrysostom.org/
Also "But at that time the Bishops were not part of Satan's conspiracy".... well... Unfortunately, we've had that problem since the start. Remember Judas, tares among the wheat, etc.