The Harvest

The Harvest is a sacrificial ritual performed by witches of the Quarter used to sustain their flow of magic from their ancestors. It involves sacrificing four teenage girls so that their magic can remain for over four hundred years. The final stage is The Reaping.

Season One
The first mention of the Reaping is in Sinners and Saints, where we learn about it through a series of flashbacks told by Davina, Sophie and Marcel. The girls, who participated were told they would be put to sleep and then be  resurrected at the Reaping. The Elders lied, as for the girls were brutally slaughtered by having their throats slit, there was even a possibility that they would not come back. Monique and 2 other girls were slaughtered before Marcel could stop the Harvest. Kieran begged Marcel to stop the Harvest in which he did. Marcel is keeping Davina hidden away, because she did not die on that night. If she dies before the Reaping, the Harvest is completed. If not, all the witches in New Orleans loses their powers.

Trivia

 * During the events of The Originals, With the exception of Agnes, Sophie, Jane-Anne, and Davina, All the other witches who were involved in the Harvest Ritual were brutally killed by Marcel and his Gang of Vampires.
 * Considering that it involves human sacrifice, it is possible that the Harvest is a form of dark magic.
 * The Harvest seems to happen every three hundred years.
 * During The Reaping, the girls needed for the sacrifice seems to be specific as four girls were chosen. There must have been some magical ritual perform to chose each girl for the sacrifice.
 * If one of the girls were to survive the sacrifice ritual, the ritual would not be complete. If it is not completed by sacrificing the remaining girl, the New Orleans Coven would begin to lose their powers and cease to be witches.
 * Each time one girl is killed, the power of this witch would pass on to the next living one as seen when Monique was sacrificed, her powers was passed onto Davina along with the power from the other two teenage witches.
 * The reason why Davina is so powerful could be because she has the power of four witches inside her including her own and from her fallen friends. Since this power was suppose to last for three hundred more years, it would explain why Davina is so powerful.
 * Each girl stands for Water, Earth, Air and Fire.