Ancient peoples connected sex to life and vitality. When they discovered that it was intercourse that caused impregnation, that is when it came to be used in fertility rites, and genitalia came to be used as symbols for fertility. This pertained to not just humans and animals, and later for crops when agriculture came about. Human sexuality has been a very important and powerful part of magical workings for tens of thousands of years.
   
In time, rites including sexual intercourse were performed at burials in order to symbolically restore life to the dead. They were anointed with menstrual blood to connect them to the womb so that they could be reborn. Likewise, they were buried underground, since the ancients believed the Underworld to be a place of magical rebirth.
   
With the knowledge of how pregnancy happened, the ancients soon learned how to prevent it. Roman women used lemon peels, which they inserted into their vaginas as a cervical cap/spermicide (lemon juice is very acidic). Egyptian women soaked a linen tampon with stinging nettle and honey. Less savory was the use of crocodile dung as a plug. Even seaweed has been used as a barrier. More effective was the use of ingested contraceptives distilled from plants. Most likely they got the idea of which ones to try by seeing how they affected the animals that ate them. For example, horse breeders know that if their animals eat ivy they will not conceive. The Romans used a species of giant fennel they called silphium, for very effective birth control. In fact, they harvested it to extinction! Also used were rue, white pepper, myrrh, cow parsnip, wormwood, pennyroyal, pomegranate, willow, and the aforementioned ivy. Some of these plant-based contraceptives have been found to be startlingly effective. Tests on lab rats have shown that some species of acacia seed and fennel to have a 100% success rate at preventing pregnancy. Mexican women have long used a species of wild yam called Barbasco root, from which researchers discovered the hormone diosgenin, which is very similar to progesterone. Combined with estrogen, this was the precursor to the first modern birth control pill.
   
One example of contraceptives in mythology is the story of Persephone (the Greek Goddess of Spring), who was kidnapped by Hades (the God the Death) and taken by him to the Underworld to be his wife. The only thing she ate there were pomegranate seeds. She did so to prevent herself from becoming pregnant from her "husband's" advances.
   
The use of contraceptives was important for magical practitioners, many of whom used sexual stimulation to raise energy. Sexual energy is the most powerful and concentrated energy raised in the physical body. Sex also has a very powerful ability to generate the altered states of consciousness necessary for magical workings.
   
Many temples in the ancient Mediterranean included priestesses who acted out the Heiros Gamos, or Sacred Marriage. These were priestesses who would accept coinage, and in return engage in divine intercourse with a person from outside the temple. This was not simply a sexual act for pay (indeed, the amount involved may not have even mattered), the man involved was making an offering to the temple in order to have the opportunity to take part in a sacred ritual. These priestesses embodied the goddess. They were her womb, her passion, her erotic nature. She assured the fertility of the land and its people, for through intercourse she was bringing the goddess' love into the human world. She might remain veiled and anonymous for the entire time, for in this act the personal was transcended and the divine entered. She created a union not only between male and female, but between physical and spiritual. She was a holy vessel whereby chthonic and spiritual forces were joined. Here we see a precursor of the modern day Great Rite.
   
One example of this is Lilith. Her recorded story begins with Innana, granddaughter of Ninlil, who was the "Queen of Heaven" in early Sumeria. The legend of Innana and Enki told of the sacred sexual customs that were one of Innana's gifts to civilize the people of Erech. Here, the holy women of the temple were known as the nu-gig, the pure and spotless virgin priestesses. They took as their lovers the members of the community who came to the temple to worship the Goddess and to receive a healing. At this time Lilith's name is recorded as a young maiden, the "Hand of Innana," who gathers the men from the street and brings them to the temple at Erech for the holy rites.
   
In the Old Religion, Witches practiced sexual rites during the solstices and equinoxes to insure the fertility of the crops and herd animals. Other rituals such as the May (Beltane) rite and the October (Samhain) used sexuality to celebrate the courtship of the God and Goddess. Some sects such as the Benandanti and Malandanti of old Italy, during the Ember Days fought mock ritual battles over the fertility of crops and herds.
   
In modern Witchcraft, sexual intercourse is considered sacred, an expression of the Sacred Marriage between the Goddess and God. For that matter the love of the Goddess for all her children, male or female. For even though 'traditional' Witchcraft is immersed in male/female polarity, that is not the only form of attraction existing in Divinity, as same-sex relationships are no less sacred or embodied by the God and Goddess.
   
Sexual intercourse is used in modern Witchcraft in The Great Rite. This is usually performed between the High Priestess and High Priest who take upon the roles of the Goddess and God respectively (though as mentioned before, this may also be performed by two women or men, who may each take the role of Goddess or God in same sex union). This is performed in a raised circle during some Sabbats and initiations. Or even at other times. It all depends on the groups and traditions involved. The Great Rite may also be done during a Handfasting (Marriage), in which case it is performed by the two being wed.
   
The Great Rite is sometimes performed only symbolically, by the high priest plunging the athame into the chalice. This is symbolic of the God entering the Goddess. Some believe that if this is so done, the rite must be later performed in actuality between the high priest and priestess. When it is done in actuality, some measure of privacy is usually given those involved. In some groups the other members walk to the edge of the circle and turn their backs until it is complete. In others they open the circle and leave the room until it is done. However, in some groups it may be performed openly due to its great significance.