Although the Summer Solstice occurs on varying dates each year, usually between the 20 and 22 June, the official date of Midsummer is designated as 24 June in the United Kingdom. As with many days of cultural significance such as Christmas, tradition held that celebrations began at sunset of the night before, making Midsummer Eve the beginning of the Midsummer festivities in ancient and medieval Britain. It was a night of superstition where it was believed the boundaries between life and death with thin, and souls would wander from their bodies and those who were due to die that year would knock upon the church door.
Midsummer Eve was also known as Saint John’s Eve, and in the Middle Ages it was a night of revelry. The local parishioners would attend church in the evening and pray, then would begin drinking and feasting, after which there would be singing and music. The church felt this was inappropriate and so from the 14th Century it was common practice for fasting to begin on Midsummer Eve, thereby preventing any boisterous celebrating. Young women would collect coal or blackened roots and place them beneath their pillows for the night, hoping to dream of their lovers.
It was customary in towns to keep a watch walking about during the Midsummer Night, although no such practice might prevail at the place from motives of precaution.Robert Chambers, The Book of Days: A Miscellany of Popular Antiquities
On the day of Midsummer Eve great pyres would be built, and then lit as the sun set. These fires would be seen for miles, and so across the horizon it was common to see fires all around. The fires were tended and kept burning until sunrise to light the way home for the souls of the living which were wandering that night, and also ward off evil spirits and appease the fairy folk and other supernatural entities. In some areas, three fires were lit together: the bonnefyre which was made of bones, the wakefyre which was wood, and Saint John’s Fire which was a pyre of both wood and bones. It was believed that eating untouched fern could make a man invisible, so young men would go out at midnight with a plate and try to harvest fern leaves without touching them. Various other herbs and plants such as Saint John’s wort, rose, and vervain were collected, as they supposedly held magical properties. These would be used on the morning of Midsummer Day to create a small effigy to bring fortune and love, called the Midsummer Man.
Midsummer Eve is noted with bonfires in parts of the country still, with localised celebrations such as Golowan in Cornwall and the fires in Peebles, though it is less notable in the contemporary calendar than Midsummer Day.