The Kotatsu is a kind of low, wooden table frame covered by a futon, or heavy blanket upon with a table on it top sits. The formation of the hori-gotatsu was slightly changed in the Edo Period during the seventeenth century. These changes consisted of the floor around the irori being dug-out into the ground in a square shape. The moveable kotatsu was created later, originating from the concept of hori-gotatsu. This kotatsu came about with the popular use of tatami matting in Japanese homes.