Cooking in clay is probably almost as old as cooking itself. The word "terracotta" means "cooked earth". In Spanish the term is "barro" - literally "mud". Hard to get much more elemental than that.
But beyond its simplicity, cooking in clay is still with us because it works so well. The clay heats slowly and evenly, perfect for anything that needs a long, slow, simmer. The flavors meld together and are somehow given a subtle earthiness from the clay, especially after the pot has been used a few times and has "seasoned".
This pot is made of natural terracotta in Badajoz, Spain, near the Portuguese border. The cream decoration on the lid is typical of the region.