Ancient HVAC, Part II: Cooling Ancient Rome


According to The Old Farmer’s Almanac, the approaching Dogs Days of summer cover the span of 40 days between July 3rd and August 11th.* Chances are good you’ve always assumed this period was referred to as the “Dog Days” because any hound worth her salt can be found chilling in a cool, shady corner until the swelter has passed. But it turns out there’s more to it…

Assuming you live in a northern latitude, step outside at dawn this time of year and just above the horizon you can spot Sirius, the brightest star in the sky. It’s commonly known as the Dog Star or Canis Major (The Greater Dog), accompanying constellations Canis Minor and Orion the Hunter as they pursue Taurus the Bull across the heavens.

The ancient Greeks recognized that beginning in July, the rise of Sirius in the sky just before the sun heralded the hottest time of the year. In fact, the Greek word “seirios” (Sirius) means glowing/burning/scorching. They believed the star radiated a searing heat that added to that of the sun to raise the temperature to somewhere near miserable. The Romans inherited this belief and declared the period to be “dies (days) caniculares (plural for puppy)” in Latin — Days of the Dog Star or Dog Days. And we’ve called it that ever since.

During the sultry Dog Days, ancient Romans would cool down at their local Roman baths. First, they’d leave their clothes in the apodyterium (think of it as an ancient locker room), then they’d sweat themselves silly in a hot bath called the caldarium, move over to a lukewarm bath called the tepidarium, and finish with a dunk in the ice-cold frigidarium — a pool often cooled by snow from the nearby Alps.

While regular folk could buy mountain ice at snow shops, Rome’s wealthy movers and shakers arranged for vast amounts of snow to be brought from the mountains right to their villas, storing it for the summer in deep wells and shafts. Nero, Rome’s most infamous emperor (A.D. 54-86), reportedly sent runners to bring him buckets of snow from which he enjoyed what were essentially snow cones flavored with fruit, juices and honey.**

20 rulers later, Emperor Elagabalus (c. 218-222) ordered 1,000 slaves to fetch snow one summer and construct a frivolous mountain of cold in his garden. Why? Because he could. He was the emperor, after all.

Which brings us to how Rome’s deep-pocketed elites and nobles cooled their homes’ interiors. Over the course of 500 years (312 BC to AD 226), Romans constructed hundreds of miles of raised stone aqueducts based on the irrigation system designs of Greece, Egypt and India. Starting at higher elevations, the aqueducts descended down into the city with about 1.5 million gallons of cold water a day at the height of the empire.

In one of the earliest forms of air conditioning, the well-to-do piped the water into their homes where channeled aqueducts inside the walls cooled the stone and surrounding air. The water passed through on its way to the city’s fountains and bathhouses to keep the commoners cool. In the end, even public squares offered some respite from the heat during the Dog Days. Molto bene!

* In ancient times at the latitudes of Greece and Italy, Dog Days would have begun near the end of July and concluded in September.

** Side note: In nearby Pompeii, ruins once buried beneath volcanic ash have turned up what appear to be shops specializing in crushed ice brought from atop Mount Vesuvius, flavored with honey — were these the first Italian shaved ices?

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