We had one when I lived in California. It was metal, about 4ft around, with a rounded bottom.
One night, I told my neighbors that I was going to have a fire in my backyard, so don't be alarmed. We thought it would be a good time to drink beer and burn up old wooden furniture.
Wellllllll, at about midnight, as we were letting the fire die down, who pops his head over my fence but a policeman.
"Whats up guys?"
"Having a little fire, but we're letting it go out now."
We had a light out there, a garden hose turned on, with nozzle...
Well, sumbiatch if the next thing I see isn't a lit-up fire truck coming down the cul-de-sac...
They came and looked around at what we had out there, and gave us the "it looks like you're having fun, buttttttttttt I don't see any food..." speech.
"Food?"
"Yeah, food..."
In the city limits, you can have an open pit fire if you're using it to cook food, and since we HAD an open pit fire and technically we weren't cooking food, we were violating a city statute.
They let us off with a warning because the hose was charged and we had a light in case anything went wrong.
The moral of the story? Check your city statutes. Most allow you to cook fire on an open pit, so keep a pack of hotdogs handy... Thats what the fireman told us to do next time.