Probably the original clay material used for pots, and ultimately cooking pots, is earthenware. Earthenware denotes clays that are mined, generally without much beneficiation (cleaning) and few, if any, added materials.

A LITTLE BRITTLE, POROUS, GENTLE HEAT, NO SOAP

Because earthenware is not fired to vitrification, it remains porous, like a flower pot. These pots may be glazed or unglazed, often handmade, some are “manufactured” in molds and presses, some built from coils and slabs. In the US, many are imported from all over the world. Given care, these pots will give lots of good cooking experiences
One legend of how earthenware came to be used is that, once upon a time, food was collected and carried in grass and reed baskets. These baskets were ultimately lined with dug up clay which makes the basket somewhat waterproof. Then, somehow one got into a fire and, lo and behold, the basket burned away and the clay was partly fired and held its shape. Some very early pots were actually made with basket designs in the clay.
Because the is little melting of the clay body in earthenware, the pots are usually somewhat porous. Early on they were used over open fires and charcoal. they would withstand the gentle heat without cracking, but they were physically somewhat fragile.
One unique feature, is that because of th3e porosity, they will soak up liquids, fats and flavors from the foods cooked in them, and pass these on the future meals. It does mean they need to be washed without soap (don’t want food that tastes soapy) and dried before putting them away.