Pithouses were built by excavating a well defined hole into the ground, usually around 6" to 18" deep but occasionally as deep as four to five feet, and creating walls and roof using a pole and adobe technology. The sunken floor of the dwelling is below the frost line and helps moderate both winter and summer temperatures, with the mass of the ground serving as an insulator. In addition, adobe walls gather heat during the day and release it when temperatures drop. The earliest pithouses were round, and varied in size between nine and twenty-five feet in diameter. Around 700, pithouse designs became more individualized. Excavations reveal examples based on squares, rectangles and shapes similar to the letter D.