This poster was used to advertise September 12th 2001's edition of the Daily Mail. It interprets the events of September 11th as being the beginning of an 'apocalypse' i.e. the end of the world as we knew it. The poster represents the feelings of uncertainty that abounded from the moment the twin towers were hit.
Some people speculated that it was the beginning of a global war; others went so far as to say it was the beginning of the end of the world. This day changed the course of history so dramatically that its effects will be felt more many years to come.
The poster also tells us something about the tendency to exaggerate events for effect. This headline is a marketing tool and it uses the language of apocalypse to heighten the sense of drama to the event.