How do you make a perfect circle in a sidewalk?

I want to have my sidewalk come out from my door and the turn 90 degrees towards my driveway. Right at the 90 degree turn I want to have a sort of large circle to put a flagpole or yard light in the middle of it. How do you go about making the circle? I thought about usin tied to little stakes criss crossing each other until I have my circle? Will this work? Or is there a more simple way of doing this? I hope you understand what i'm doing here, It's kind of hard to explain, but any help on this matter would be greatly appreciated.