Rocks?

1/34 Rocks let rain drain though, if you are constructing a fire ring. Soggy ashes aren't much good. Rain will also dissolve the ashes making lye and draining out assuming you use wood. And air circulating along the ground and up into the fire, make it hotter and burns most or all the wood, a natural draft. Keeping air flowing in under the fire will take some maintenance. At a campground a pair of nitrille gloves is just about a necessity to clean out cans and garbage,dg droppings, plastic everything and glass bottles and cigarette butts. left by the........... Nothing much worse than burning stinking garbage.
As far a large rocks maybe the fire ring is supported on them, a good idea but I haven't seen it.

I put rocks in campfire to heat them so I can place them at the foot of my bed to warm my toes

Here is a good reason for rocks in the ring.



Very tall ring with no air holes at the bottom. Need to raise the wood so it can get air to burn properly.

I can think of one POSSIBLE reason. Those heavy steel and concret rings it's hard to let the fire 'Breath' (I use a forced air thing I had custom made)

Rocks may lift the logs to let air in at the bottom

But I also support the other response (To mess with maintenance)

In theory, putting rocks UNDER the steel ring itself allows more air to come into the fire pit area instead of the fire smothering for air. (In theory, air can draw from the bottom of the ring causing a better draft, thus creating a stronger fire). Actually, I think it's just inexperience on the camper's part and green wood.

What's sad then, rather than taking the rocks out of the fire pit when done and letting the ring rest back on the ground, they simply kick the rocks on into the fire pit leaving them .... yes ... making it more difficult on the next person to use the fire pit cleaning out the ash.

But, I'll take rocks over cigarette butts any day. Anyone who throws cigarette butts into a fire pit needs their own butt kicked! They don't burn, and they are NOT bio-degradable. Someone ELSE has to eventually pick them up. Nasty A-holes!

They are put in the fire rings to mess with the camp host who will need to remove them to clean the pit.

JimR