Whether involved in architecture or not, most readers likely picture the pit dwellings of Japan's Jomon period, often described as the country's earliest form of habitation, as having thatched roofs laid low over the ground. This is only natural, as such forms are how the dwellings are depicted in history textbooks and reconstructed at archaeological sites across the country.

Over roughly the past 30 years, however, advances in archaeological excavation and comparative studies with examples from around the world have made it clear that this understanding is mistaken. In the first place, with the polished stone tools of the Jomon period, thatches could not have been harvested.

If not thatch, what form did the roofs take? The roofs are now understood to have formed gentle, grass-covered mounds rising from the ground, with a thin layer of soil beneath the grass, followed by bark as a waterproofing layer, and a framework of rafters and logs supporting the structure. In Japanese archaeology, this type of roof is known as tsuchibuki ("earthen roofing"), but since what one actually sees from the outside is not the earth itself but the grass—serving as turf—that prevents the soil from washing away, I would suggest that it is more fitting to call it shibabuki ("turf roofing").

Such turf-roofed houses may be described as dwellings enveloped in earth: the sunken floor is earthen, the low rising walls are earthen, and the roof, beneath its grassy surface, is likewise formed of soil. Remarkably, known as turf houses, houses of this kind remained in use in Iceland until relatively recent times, having been inhabited for more than ten 10,000 years, from the Neolithic era through the 20th century.

Iceland, surely among the northernmost and coldest regions ever settled by humans, is an island at the northern edge of the North Atlantic. Even today, ice caps that persist through summer cover parts of the land. Grass grows, but trees are scarce, and in earlier times people are said to have gathered driftwood to build their homes. The principal industries were fishing and sheep farming, with wool as the main source of income. Their food staples were potatoes and beans grown on the limited plots of land available for farming, along with abundant fish and mutton.

The first settlers in the Neolithic period are thought to have come from Scotland. From the 14th century, the island became a Danish colony, eventually gaining independence in 1944.

After landing at the airport in Reykjavík and spending a night there, I hired a taxi early the next morning and drove clockwise around the island for about 4 hours. There were no fields in sight; at intervals of roughly an hour, small settlements dotted with buildings appeared, surrounded by sheep and cattle grazing on the grass.

When I asked the driver—who seemed to have guessed from my destination what I had come to see—how recently such houses had been lived in, he replied, "My parents' house was like that, and there were many until not so long ago."

Among the many turf-roofed houses that have been rapidly abandoned in recent years, the Glaumbær turf houses have been preserved in their original state due to their historical significance and excellent condition.

There is a reason why this particular complex alone has survived so well. In the 17th century, a wealthy Englishman on an expedition recognized its significance and subsequently provided financial support to ensure its preservation.

When I first glimpsed the buildings through the car window, I was struck by the importance of windows. Without them, one might easily mistake the complex for a rural waterworks facility or simply a series of earth mounds. The windows are unmistakable signs of human life within.

Looking more closely at the sides of the buildings, one can see that the walls are built up in layers resembling blocks about the size of concrete masonry units. These are formed from compressed, withered grasses intertwined with fine roots. The marsh vegetation that spreads across the surrounding wetlands does not readily decay in the severe cold, even after dying back in winter; instead, it accumulates over ten or twenty years, becoming a semi-carbonized, porous, soil-like material. Cut into blocks with an edged tool, this material was stacked to form walls and laid over rafters as roofing material. In Japan, earthen roofs would have used bark—such as that of cypress or white birch—as a waterproofing layer, but here no such layer appears necessary. Presumably, the thick strata of former grasses draw infiltrating moisture downward by capillary action, directing it into the walls and ultimately into the ground.

Circling to the south side, one finds, somewhat unexpectedly, a row of six gabled roofs, their gable ends constructed not of turf but of painted wooden boards. According to local studies, the history of these buildings is well documented: as of 1681, this row extended further than it does today and was composed of three connected units. This portion alone had wooden walls. Earlier examples known from excavations suggest that the entire complex was once earthen, with entry and exit likely through roof openings.

As long as the hearth fire was kept burning, the interiors remained not only warm but also dry, allowing the inhabitants to pass the winter and make it through to spring. Fuel could be obtained from the semi-carbonized layers of former grasses. It could get a bit smoky, but that was just part of the deal.