Caldas de Reis is a municipality in Galicia, Spain in the north of the province of Pontevedra.
In Ptolemy's Tables, the town appears as Aquae calidae and in the Itinerarium Antonini as Aquae Celenae. Lucas de Tuy calls it Caldas de Rege. F. Pérez calls it Cilenos or Celenae.
A bishop of this see named Ortigius was at the first Council of Toledo at the end of the 4th century. Of two bishops consecrated later, named respectively Pastor and Siagrius, one appears to have been for this diocese.
In the mid-6th century, the bishop's seat was transferred to Iria Flavia, now the archdiocese of Santiago de Compostela. Thus, no longer a residential bishopric, Caldas de Reyes is today listed by the Catholic Church as a titular see.
The town is the second to last stop on the Portuguese Way path of the Camino de Santiago before it reaches Santiago de Compostella.