Natatio

The natatio (plural: natationes) was a large, open air bathing or swimming pool. The name is derived from the Latin nato, to swim. The term is rather vague and can refer to a number of structures with different specific purposes. Natatio is not usually used to refer to the pool in one of the bathing rooms with a specific function (such as the frigidarium, caldarium, or tepidarium), but rather may be present as a separate feature of a bathing complex not associated with one of the purpose-built bathing rooms, though. It is typically rectangular in shape and rather shallow in comparison to modern swimming pools, usually only a meter or so in depth at most. In some cases, a natatio may be fed by a thermal or non-thermal spring, providing it with water of a particular temperature, but was not typically heated by artificial means.

In addition to being a feature of a bathing complex, there are also examples of natationes being built in private residences and not necessarily associated with bathing areas inside these residences. While some structures identified as natationes in private residences seem to have been mostly decorative, the presence of steps inside some of these pools would seem to indicate that they were indeed used for recreational purposes, rather than solely as decoration.