Then they drew a circle in the snow that was from 9 to 15 feet in diameter. With long knives, they cut angled snow blocks from within the circle and stacked them so the walls spiraled inward. This makes the walls stronger. A narrow doorway is left - just large enough for a person to get through, but too small for a polar bear. Soft snow is packed into the cracks to keep out the wind.
Skilled builders can make an igloo in about an hour.
If the igloo is to be a more permanent dwelling, small, translucent windows are added, made of seal intestines or sheets of freshwater ice. The heat slowly changed the snow walls to ice within a few weeks. In the 1800s, the United States government gave free plots of land to anyone willing to build a house on it and live there for five years. The land was in the Midwest and West. The people who settled the land were called homesteaders.