Witches’ sabbath (or sabbat), nocturnal gathering of witches, a colourful and intriguing part of the lore surrounding them in Christian European tradition. The concept dates from the mid-14th century when it first appeared in Inquisition records, although revels and feasts mentioned by such classical authors as the Romans Apuleius and Petronius Arbiter may have served as inspiration. The sabbath, or sabbat, derived probably from the term for the seventh day used by the Jews, might be held on any day of the week, though Saturday was considered rare as being sacred to the Virgin Mary.
Reports of attendance at sabbaths varied; one confessed witch reported a gathering of 10,000. Witches reputedly traveled to the sabbath by smearing themselves with special ointment that enabled them to fly through the air, or they rode on a goat, ram, or dog supplied by the devil. Favourite locations included the Brocken, in the Harz Mountains, Germany; the Bald Mountain, near Kiev, Russia; the Blocula, Sweden; and the Département du Puy-de-Dôme, Auvergne, France. Typical dates included the two traditional Druid festivals, the eve of May Day (April 30) and All Hallows Eve (October 31), and the seasonal festivals of winter (February 2), spring (June 23), summer (August 1), and fall (December 21).
Occurrences at the sabbath were represented by inquisitors as including obeisance to the devil by kissing him under his tail, dancing, feasting, and indiscriminate intercourse.
[From Encyclopedia Britannica]