What were the ancients trying to accomplish with circumcision?

It is an old custom/ritual- thousands of years old. Somebody thought that it was important for some reason. What is that reason?
Since I am circumcised, I assume I benefited in some really big way from the procedure. I am not Jewish, but I figure Jews probably know. Give it up please.
Is this a social question, or a general question. I figure its not a meta question.