Why did some WW1 planes have three wings?

You may have noticed that some WWI fighter planes had three wings, but why was this? Did the extra wings help make the ...
Kotaku

Dogfight 2 : The Great War

All the Latest Game Footage and Images from Dogfight 2 : The Great War Dogfight 2: The Great War is a arcade flight game where players pilot historical planes (Spitfires, Mustangs, Messerschmitts) ...