Short version: it is an oversized wicket barrel with an added steep roof. Pretty neat. Instead of a ring, a similar structure Can be made by interlacing wickets

Short version: it is an oversized wicket barrel with an added steep roof. Pretty neat. Instead of a ring, a similar structure Can be made by interlacing wickets with the frame. Can be daubed too if you need more insulation and permanence. This simplicity and effectiveness is why it is ancient yet still used now.