Socrates was a famous teacher in ancient Athens. He wanted his students to question things. "Is our government good? If gods exist, where do they live?"

This angered some of the wealthy nobles in ancient Athens, not many, but a few. They accused Socrates of mocking the gods. They demanded a trial. If found guilty, anyone who mocked the gods would be killed. This was a severe charge. 

In ancient Athens, anyone could demand a trial. Whichever side lost the trial paid for the whole trial. You did not bring charges unless you had lots of proof or lots of wealth. These men had wealth.  

Socrates thought it was ridiculous. He could not believe that anyone would find him guilty. He refused to defend himself. If he had presented a defense, the jury most probably would have found him innocent. But, since he said nothing, the jury had no choice but to find him guilty. 

If you were found guilty in ancient Athens, the punishment was death. Rather than have the citizens of Athens kill him, Socrates took poison and died. He was seventy years old at the time.