The most spectacular pictures of Earth Hour 2012

The lights were out in the Acropolis of Athens for Earth Hour, and it wasn't alone.

World landmarks such as the Great Wall of China and the Notre Dame Cathedral in Paris went dark for 60 minutes to join Earth Hour on Saturday March 31.

Earth Hour, in which 147 countries have united, was started by the WWF (World Wildlife Fund) and has been running for six years. A global call to action to individuals, businesses and governments to unite, it is the largest environmental event in history.

As Earth Hour made its way around the globe, hundreds of millions of people united to demonstrate that we urgently need to take action to protect our planet.