Frigidarium
The vaulted ceilings and windows of the frigidarium of the Baths of Diocletian.
The massive frigidarium was the first true bathing room which bathers would visit after coming in from outdoor athletics or swimming in the pool. In the Baths of Diocletian, the frigidarium was the most visually impressive room, featuring especially high vaulted ceilings supported by external buttresses. Eight large columns were set around the perimeter of the main part of the room. The ceiling was originally 30 meters high (some height has been lost in modern day due to a raised floor).1
Bathers immersed themselves in a pool of very cold water before moving on to the tepidarium.
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1. Amanda Claridge, Rome (Oxford: Oxford University Press, 1998), 394.