A frigidarium is a large cold pool of Roman bath

Thermae

In ancient Rome, thermae and balnea were facilities for bathing...

s. It would be entered after the Caldarium

Caldarium

right|thumb|230px|Caldarium from the Roman Baths at [[Bath, England]]. The floor has been removed to reveal the empty space where the hot air flowed through to heat the floor....

 and the Tepidarium

Tepidarium

The tepidarium was the warm bathroom of the Roman baths heated by a hypocaust or underfloor heating system.The specialty of a tepidarium is the pleasant feeling of constant radiant heat which directly affects the human body from the walls and floor.There is an interesting example at Pompeii; this...

, which were used to open the pores of the skin. The cold water would close the pores. There would be a small pool of cold water or sometimes a large Swimming pool

Swimming pool

A swimming pool, swimming bath, wading pool, or simply a pool, is a container filled with water intended for swimming or water-based recreation. There are many standard sizes; the largest is the Olympic-size swimming pool...

 (though this, differently from the piscina natatoria, was usually covered). The water could be also kept cold by using snow.

The frigidarium was usually located on the northern side of the baths. The largest examples of frigidarium were both in Rome: that of the Baths of Caracalla

Baths of Caracalla

The Baths of Caracalla in Rome, Italy were Roman public baths, or thermae, built in Rome between AD 212 and 216, during the reign of the Emperor Caracalla.- History :...

, located soon after the entrance, measures 58 x 24 m, and that of the Baths of Diocletian

Baths of Diocletian

The Baths of Diocletian in Rome were the grandest of the public baths, or thermae built by successive emperors. Diocletian's Baths, dedicated in 306, were the largest and most sumptuous of the imperial baths. The baths were built between the years 298 AD and 306 AD...

, covered by a cross vault. Some, like one in Pompeii

Pompeii

The city of Pompeii is a partially buried Roman town-city near modern Naples in the Italian region of Campania, in the territory of the comune of Pompei. Along with Herculaneum, Pompeii was destroyed and completely buried during a long catastrophic eruption of the volcano Mount Vesuvius spanning...

, had a circular plan.