The oven opening was closed with a large stone, sometimes sealed with clay.
Ovens which worked on this principle, but were constructed of bricks or small stones, may still be seen in the ruined city of Pompeii.
The Jews also had fixed ovens in some of their houses, frequently in the main rooms.
These ovens or hearths took the form of clay-covered hollows in the floor which were heated with burning wood.
The upper part, accessible from the top, was the baking chamber.
Some historians believe it is possible that brewing began when the first cereal crops were domesticated.But there is an alternative and even more likely theory-that on some occasion ale instead of water was used to mix the dough.The rise would be more spectacular than from a few errant spores and the effect would be easy to explain and equally easy to reproduce." ---Food in History, Tannahill (p.Indeed, there are scholars who have theorized that a taste for ale prompted the beginning of agriculture, in which case humans have been brewing for some 10,000 years...Most archaeological evidence, however, suggests that fermentation was being used in one manner or another by around 4000 to 3500 B. Some of this evidence-from an ancient Mesopotamian trading outpost called Godin Tepe in present-day Iran- indicates that barley was being fermented at that location around 3500 B. Additional evidence recoverd at Hacinegi Tepe (a similar site in southern Turkey) also suggest that ancient Mesopotamians were fermenting barley at a very early date...For six thousand years and more it is the oven, however crude or complex, which has transformed the sticky wet dough into bread.It is the oven which influences the final character of the loaf; the effieciencycy of an oven, or lack of it, can determine the success or failure of any bread baker's business. It was the Egyptians who first used a manufactured portable oven.In Ancient Rome bread ovens in the public bakeries were originally hewn from solid rock.These ovens were heated by the familiar method of burning wood in the baking chamber, raking out the ashes and putting in the dough to bake.At some stage in the Neolithic era people had learned that if, instead of using ordinary grain, they used grain that had been sprouted and then dried, it made a bread that kept unusually well. The Egyptian process was to sprout the grain, dry it , crush it, mix it to a dough and partially bake it.The loaves were then broken up and put to soak in water, where they were allowed to ferment for about a day before the liquor was strained off and considered ready for drinking." ---Food in History, Reay Tannahill [Three Rivers Press: New York] 1988 (p.48) "Leavening, according to one theory, was discovered when some yeast spores--the air is full of them, especially in a bakehouse that is also a brewery--drifted onto a dough that had been set aside for a while before baking; the dough would rise, not very much, perhaps, but enough to make the bread lighter and more appetizing than usual, and afterwards, as so often in the ancient world, inquiring minds set about the task of reproducing deliberately a process that had been discovered by accident.