how different is it from the ancient games?
In the ancient games, the competition was among representatives of several city-states and kingdoms of Ancient Greece. Whereas the modern games are international nature.
Olympic Games
The Ancient Olympic Games were religious and athletic festivals held every four years at the sanctuary of Zeus in Olympia, Greece. Competition was among representatives of several city-states and kingdoms of Ancient Greece. 
how does an athlete get to participate in the olympic games All professional athletes are eligible for the Olympics, subject to the approval of the IFs. what are these games? he modern Olympic Games or Olympics are leading international sporting events featuring summer and winter sports competitions.
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Olympic Games [SEP] Ancient Olympics
The Ancient Olympic Games were religious and athletic festivals held every four years at the sanctuary of Zeus in Olympia, Greece. Competition was among representatives of several city-states and kingdoms of Ancient Greece. These Games featured mainly athletic but also combat sports such as wrestling and the pankration, horse and chariot racing events. It has been widely written that during the Games, all conflicts among the participating city-states were postponed until the Games were finished. This cessation of hostilities was known as the Olympic peace or truce. This idea is a modern myth because the Greeks never suspended their wars.