These are commemorated by many Christian denominations, such as the Roman Catholic Church, Lutheran Churches, and Anglican Communion. In Sweden the Midsummer is such an important festivity that there have been serious discussions to make the Midsummer's Eve into the National Day of Sweden, instead of June 6. It may also be referred to as St. Hans Day.
Saint John's Day, the feast day of Saint John the Baptist, was established by the undivided Christian Church in the 4th century AD, in honour of the birth of the Saint John the Baptist, which the Gospel of Luke records as being sixth months before Jesus. As the Western Christian Churches mark the birth of Jesus on December 25, Christmas, the Feast of Saint John (Saint John's Day) was established at midsummer, exactly sixth months before the former feast.
By the sixth century, this solar cycle was completed by balancing Christ's conception and birth against the conception and birth of his count, John the Baptist. Such a relationship between Christ and his cousin was amply justified by the imagery of scripture. The Baptist was conceived sixth months before Christ and his cousin as amply justified by the imagery of scripture. The Baptist was conceived six months before Christ (Luke 1:76); he was not himself the light, but was to give testimony concerning the light (John 1:8–9). Thus John's conception was celebrated on the eighth kalends of October (24 September: near the autumn equinox) and his birth on the eighth kalends of July (24 June: near the Summer solstice). If Christ's conception and birth took place on the 'growing days', it was fitting that John the Baptist's should take place on the 'lessening days' ('diebus decrescentibus'), for the Baptist himself had proclaimed that 'he must increase; but I must decrease' (John 3:30). By the late sixth century, the Nativity of John the Baptist (24 June) had become an important feast, counterbalancing at midsummer the midwinter feast of Christmas. —Professor Éamonn Ó Carragáin, University College Cork
Within Christian theology, this carries significance as John the Baptist was "was understood to be preparing the way for Jesus", with John 3:30 stating "He must increase, but I must decrease"; this is symbolized in the fact that the "sun begins to diminish at the summer solstice and eventually increases at the winter solstice." By the 6th century AD, several churches were dedicated in the honour of Saint John the Baptist and a vigil, Saint John's Eve, was added to the feast day of Saint John the Baptist and Christian priests held three Masses in churches for the celebration.
In Florence, medieval midsummer celebrations were "an occasion for dramatic representations of the Baptist's life and death" and "the feast day was marked by processions, banquets, and plays, culminating in a fireworks show that the entire city attended." The historian Ronald Hutton states that the "lighting of festive fires upon St. John's Eve is first recorded as a popular custom by Jean Belethus, a theologian at the University of Paris, in the early twelfth century". It is possible that this was a Christianization of fires that were formerly lit in honour of Hercules, before Christianity arrived in Europe. However, in England, the earliest reference to this custom occurs on in the 13th century AD, in the Liber Memorandum of the parish church at Barnwell in the Nene Valley, which stated that parish youth would gather on the day to sing songs and play games. A Christian monk of Lilleshall Abbey, in the same century, wrote:
In the worship of St John, men waken at even, and maken three manner of fires: one is clean bones and no wood, and is called a bonfire; another is of clean wood and no bones, and is called a wakefire, for men sitteth and wake by it; the third is made of bones and wood, and is called St John's Fire.