24 June 1868,
The Basque assemblies asked the Pope to declare a holiday this day. San Juan Day is a great celebration in the towns of Euskal Herria. Both the washing with water and the day before the fire is celebrated. It originates from the summer solstice celebrations in the northern hemisphere. It is also celebrated in other countries of the world, especially in Europe.
Source:
Koldo Izagirre. History of the Basque Country Donostia (1800-1998) (Susa).