Just came across these pics of an abandoned section of Beirut which got me doing a quick bit of research. What was the Green Line and why was it abandoned...

Green Line, Beirut 1982

The Green Line was a line of demarcation in Beirut, Lebanon during the Lebanese Civil War from 1975 to 1990. It separated the mainly Muslim factions in West Beirut from the Christian Lebanese Front in East Beirut. The appellation refers to the coloration of the foliage that grew because the space was uninhabited. Many of the buildings along the Green Line were severely damaged or destroyed during the war. 

So while most of the buildings are no longer abandoned due to a huge urban renewal project in Lebanon following the war, these photos are some pretty awesome evidence of just how in the space of a short number of years vegetation can engulf abandoned cities. I can never get enough of this stuff.