Experience verifies my assertion. Before Christianity had abolished civil slavery in Europe, working in the mines was judged too toilsome for any but slaves or malefactors:
Horrexek pentsarazten dit honela: kristautasunak Europan morrontza zibila abolitu aurretik, meategietako lanak hain gogortzat jotzen ziren, non uste baitzen ezin zirela egin esklaboen edo delitugileen bidez ez bazen.