Houses of the Iron Age were built with a louvre - an opening in the roof above the firepit to let the smoke out and a bit of daylight in. If the opening was placed in the gable, it was called an ‘owl hole’.
The exterior walls were built with peepholes - small openings where light could enter. To provide protection from wind, cold weather and rain, the openings could be covered with translucent materials such as animal hide or pig’s bladder.
On the Danish island Læsø it is still possible to find houses with louvres hidden in the roofs.