Early Refrigeration

I had known for a while that certain ancient peoples, supposedly including the Persians and Romans, used preserved ice in the summer for cooling drinks (for the wealthy) and making special treats, but I'd always assumed that this was a some time thing, depending upon weather conditions and how carefully you tended your cave or storage cellar or whatever.

Yakhchāl, courtesy of Wikimedia Commons

Recently, I learned that the technology used for this purpose at least by the Persians (I don't know what the Romans did) was much more sophisticated than a cave or pit, and was quite effective. The Persians built structures called yakhchāl for the purpose of keeping ice and perishable foods. Yakhchāl literally means "ice pit," but what the Persians did was more sophisticated than a hole dug in the ground to store ice. This article explains how they were built and how they worked. The spiral tracks channel water from evaporation and melt water to the bottom where it can refreeze at night, when the desert is cold.  Often, the yakhchāl was adjoined by a separate structure that directed windflow over the ice, chilling the chamber.  The main building material for the yakhchāl--mud.

A truly elegant solution to the problem of keeping foods cold--solved with Bronze Age technology.