Roman Leather Lamellae Scales from Karanis, Egypt

[Dan Howard]

"Made from earthenware, bronze, or iron, the clibanus, often preheated, was used to cook not only bread but also meat. Literary and archaeological evidence from places like Cosa, Pompeii, and Rome show that the clibanus was round or domed-shaped and wider at the bottom than at the top."

Ancient Food Technology - Page 368
Robert Irvin Curtis - 2001

Not a big leap of imagination from a bronze or iron box to a cuirass of some sort.

It isn't a box; It is a dome - it looks kinda like an igloo. It can cook meat but not by baking. The meat is placed on the outside surface (just like dough) and it is barbequed.