For hundreds of years Native Americans in the Southwest made bread in simple adobe ovens. Not only are these ovens fairly easy to make and environmentally friendly, they make amazing bread due to their thermal mass and slow baking abilities. A well built adobe oven with a shelter over it to keep off the rain can last indefinitely.
Build a Base for the Oven
Place large stones in a circular ring on the ground, roughly 4 feet in diameter.
Build this ring into a strong wall about 1 foot tall, then fill the inside of it with soil, sand, or rubble, packed and tamped down tightly.
Smooth out the top with tightly packed sand or adobe mixture.
Build the Basic Oven Structure
Lay two layers of brick or stone on the platform where you are building the oven. This is the floor of your oven.
Lay the adobe bricks around this central area, holding them together with more of your soil and sand mixture, or with mortar. Carefully build this structure up while narrowing its diameter, until you have closed the top and have created an enclosed oval shape.
Leave a one foot wide arch at one end for the door. Place a small vent at the top of the structure.
Cover With Finish Coat
Extend the arched doorway with more bricks or with stones, so the oven now looks like an igloo with a small doorway.
Cover the interior and exterior surfaces with more soil and sand mixture.
For this final coat, make the mixture slightly wetter so that it will easily fill any gaps or cracks between the bricks.
As an alternative to using adobe bricks, you can simply build the oven directly with the mixture of sand, soil, straw, and water (cob), forming the oven shape with your hands.