The Night of San Juan is a festival of pagan origin, not very old that is often linked to light fires or fires, linked with celebrations on the arrival of the summer solstice in the northern hemisphere, whose principal rite celebrated is light a fire.
The purpose of this ritual was to "give more power to the sun", that from those days, was becoming "weaker"-the days are getting shorter until the winter solstice.
Symbolically fire also has a "cleansing" function in people watching him.
It is celebrated in many parts of Europe, but is particularly strong in Spain, Portugal (Fogueiras de São João), Norway (Jonsok), Denmark (Sankthans), Sweden (Midsummer), Finland (Juhannus), Estonia (Jaanipäev) and the UK (Midsummer).
Source: Wikipedia/Fotos: Diego Antonio Crespo-Cabrera Rojo