What is the tradition of Midsummer Night?
Pan-European Midsummer traditions, according to Frazer's Golden Bough (62:5), include the casting of herbs, pebbles or effigies into a bonfire to ward off bad luck, leaping over or dancing around that fire to increase the fertility of the people and the land, and the igniting of hay bundles and wooden cartwheels, which were then rolled down a hill, as an oracular means of predicting the success of that summer's harvest. Midsummer, as the turning point of the year, represents a liminal period. It is a time where past actions are reflected upon and the fruit of their actions are considered and anticipated. It is a mid-point; a brief resting place where hope is at its highest and the results of ones past actions can equally go in or against ones favour. It is a beginning and an end at once, and is part of the ongoing cycle of death and life as represented by the death of Baldur, the myth of Ragnarök, or the cyclic feud between Arawn and Hafgan - the Holly King and the Oak King.
Shakespeare, we assume, gave it its title. The play is full of allusions to the story being "no more yielding, but a dream". The lovers and Bottom remember their night in the forest as a dream. And why midsummer? It's the shortest and warmest night of the year, and a night traditionally associated with magic.