The Romans named it Aquae Iasae, after the tribe Iassi, who settled this area between Varaždin and Daruvar from the 8th century B.C. They chose the places with thermal springs for their settlements. Therefore around twenty geothermal springs can be found in the area they settled- from Rogaška Slatina in the west to Daruvarske Toplice in the east, including all the spas in Zagorje- Varaždinske Toplice, Krapinske Toplice, Stubičke Toplice and Tuheljske Toplice.
An ancient phonem „ias“ can be found in its name, which means to boil, so the name Aquae Iassae coul be translated as „warm spa“, and the Iassi as „the tribe that lives near warm healing springs“.
The Iassi obviously knew a lot about healing and could heal with warm water and healing mud. They knew how to treat wounds, remove pain and treat infertility so they were famous as „healers“ even outside the area they settled. The Iassi had had a centuries- long experience in healing when the Romans came to these areas and started building thermal spas and settlements around the thermal springs.
Thanks to the healing sulphuric water, Aqua Iasae became the healing place for Roman legionaries and higher officers, so it was allegedly visited by the Roman Emperor Caracalla (188-217), who ordered the construction of the famous spa in Rome.
Healing properties of this water were also recognized by the Croats who probably arrived here in the 7th century, 300 years after the Roman settlement was devastated in the Great Migration. They built a new settlement there and called it- Toplice (* English= spa).