The earliest hot tubs were calderas in which hot stones were placed to heat the water.
Therma in Ikaria has been a very popular place particularly for hydrotherapy ever since the 4th century BC.The remains of wrecked marble bathtubs along with a pre-historic aqueduct that have been unearthed from this area bear ample testimony of the place’s popularity in the ancient times.
In 737 A.D., Japan’s first onsen opened near Izumo, Shimane, and centuries later the first ryokan (inns) were built, offering food, accommodations, and soaking tubs called ofuro.
In ancient Rome there were three types of baths: baths at home (balnea), private baths (balnea privata), and public baths (balnea publica). The practice of bathing was so engrained that the Roman legions, during their long occupations in foreign lands, built their own baths at mineral and thermal springs in the newly conquered lands. Examples are found all over Europe.
After the fall of the Roman Empire in 476 and the rise of Christianity, cleanliness was abandoned since the Church considered that the practice of bathing a prelude to forbidden behaviour.
At Cluny custom required monks to take a full bath at Christmas and Easter. Private bath-rooms in castles, such as the one at Leeds, could often accommodate multiple bathers. From the 13th century onwards, baths gradually came into re-use, particularly in southern Europe under the influence of the Moors.
The 1940s hot tubs began to appear in the USA, inspired by the Japanese ofuro. Hydrotherapy pumps were introduced by Jacuzzi. Fiberglass shell hot tubs appeared around 1970 and were soon superseded by cast acrylic shells.
The first Hot Tubs in Scotland appeared around the 1990’s and have increased in popularity ever since.