A concert of the 23rd World Congress of Philosophy is held at Odeon of Herodes Atticus at the foot of the Acropolis hill in Athens on Aug. 4, 2013. The 23rd World Congress of Philosophy is opened on Sunday evening. The international meeting which is organized by the International Federation of Philosophical Societies every five years is hosted in Greece for the first time in a difficult period for the debt-laden country and several countries across the globe. [Photo/Xinhua]