Wikipedia describes the Summer Solstice as a celebration since ancient times, an astrological event and a time of mystery and religious fervor.  People once believed that mid-summer plants had miraculous healing powers so they were harvested on this night.  Bonfires were lit to protect against evil spirits which were said to roam freely when the sun was turning southwards. Later, witches were thought to be on their way to meetings with other evil powers.  In Sweden there were sacrifices in the name of fertility.  Christianity used this time to venerate saints such as 5^th Century St. Elegius, patron of goldsmiths, or more broadly, St. John the Baptist.  On a more secular plane, Hindus named their summer day, Dakshinayana, and celebrated it in mid-july.  Setisbun is a word used by the Japanese to commemorate the start of all four seasons.  But whatever the notation, each change is marked as an important event.