The Sant Grau Roman thermal baths were constructed around the year 50 AD over a previous thermal spa from the 2nd – 1st centuries AD. Conversely, the 1st century AD building is preserved in a way that is notably complete. The basic element was the large rectangular central pool (natatio) measuring 26 by 22 feet and with graduated access.
In the 2nd century BC, from the early times of the Roman period, the existence of Caldes thermal waters encouraged the start of significant thermal spa activity that led to the formation of a small town centre around it.
The central room of the east wing is one of the most important rooms in the entire thermal spa. Its importance lies in the fact that it is where the thermal water that gave life to the whole complex came from in Roman times.