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.

The Empire State Building in New York also joined this initiative. 

The Eiffel Tower, Arc de Triomphe and Notre Dame Cathedral in Paris went out (although the tower lights went out for five minutes for security reasons). 

In China, the lights illuminating the ancient Great Wall near Beijing went off for 60 minutes, in an initiative which totaled some 120 cities of the country. 

In New Delhi, India, candles were lit to celebrate 'Earth Hour'. In addition, the presidential residence was darkened, as well as the Rashtrapati Bhavan, India Gate and the historic Red Fort. 

The entrance of the famous Luna Park in Sydney, Australia, also turned off their lights. 

In Greece, the monumental Acropolis turned off its lights, as did other buildings in the capital such as the Parliament, the famous Grand Bretagne Hotel and all the municipal buildings of the City . 

The Sagrada Familia in Barcelona was left in blackness, as was the Royal Palace of Madrid and the Alhambra in Granada.