The Romans soon realised the benefits of the hot water that flowed naturally into what is now Caldes de Montbui. Which is why they founded a spa resort here that, even today, remains an exceptional testament, with the baths located right in the heart of the town. They are the most well preserved in the Iberian Peninsula.
The restored section – where you can see a pool, 13.5 metres by 6.9 metres, made with opus signium and covered by a vault - is just one of the wings of the large thermal bathing facilities built in the Imperial era. The town of Aquae Calidae grew up around it (although there is controversy about whether this name refers to the current Caldes de Montbui or to Caldes de Malavella), which was a major power in the 1st century AD. The remains of villas have also been found, dotted around the outskirts.

After the Romans, the town of Caldes went into decline, although it remained populated into the Visigothic era. Thermal bathing was brought back in the 19th century, when Caldes de Montbui became the second spa resort in Spain.