Ol Gabe,
Good question!
I will try to answer to the best of my knowledge.
That "Black Iron"(cast iron) type of pot is quite old, just how old I do not, quite honestly, know for sure.
The "rings" are a method of casting structural strength, added support, into the cast iron, which was quite fragile.
Some of these pots (cauldrons) could be very large. Large enough to scaled a hog to help remove the hair before butchering.
Broken parts and piece of black iron pots (of approximately the size shown in the images) have ben found in association with the early Jamestown Settlement/Plantation system, from the early 1600's Virginia Colony.
Although this is somewhat brief, I hope it help adders your question.
My best,
Blair