Derived from the Persian words for “ice pit,” a yakhchal was a mound made of mud, rising as high as 18 meters (60 ft) off the ground. A pit up to 5,000 cubic meters (175,000 cu ft) in volume would then be dug underneath it. Using a process known as evaporative cooling, wind would blow into the pit, chilling any water which was brought in or left behind by melting ice. The ice itself was made in channels that extended behind the yakhchals that were filled with water at night, when temperatures dropped below freezing. The ice that formed at the top of the channels was then chipped off and put into the yakhchal. Known to the inhabitants of present-day Iran since as far back as the 17th century B.C., these “freezers” are much larger than those found farther west.Though fairly efficient in their ability to store ice, yakhchals quickly fell out of favor when electric refrigeration was invented. Modern freezers also tended to produce much cleaner ice, as dust and other contaminants would often enter the water in a yakhchal. This is probably due to the fact that they were normally made of brick and mud.