The first , about the end of the world , was written when he was only 20 . Savonarola wrote the second poem `` De Ruina Mundi '' ( `` On the Downfall of the World '' ) in 1475 . His stance against morally corrupt clergy was initially manifested in his poem on the destruction of the world entitled De Ruina Mundi ( On the Downfall of the World ) , written at the age of 20 .