|Night of Aeolus|
Once every hundred years
The elementals must gather to perform the Ritual of the Guardians to save the world.
The Night of Aeolus takes place every hundred years, whereby four Elementals, i.e. a Firestarter, a Waterbearer, an Earthshaker and a Windwalker, come together to perform a ritual in the Circle of Gaea. This ritual is to calm the turmoil that the world undergoes every century. The Circle of Gaea changes place every century though there is one similarity in all the locations: they are all in nature and have a pentagram. Also, to perform the ritual, a wand, a sword, a chalice and some coins need to be handed out to the Elementals; the sword and the wand are interchangeable between Air and Fire, the chalice to Water and the coins to Earth. To fill in the fifth spot on the pentagram, a Spirit Elemental is required. A Spirit Elemental is a pure human who is not "suppressed by magical powers", whose power is 'represented' by nothing more than his own purity of heart. Unlike the other Elementals, he finds them on his own.
When the Charmed Ones assisted in the Night of Aeolus, they recruited their old charge Tyler Michaels to serve as the Firestarter after the original Firestarter died, gathering the other two elements—windwalker Rafe and waterbearer Gabrielle Chambers—with the aid of earthshaker Muriel Hammond; the Halliwells' mortal ally Darryl filled the role of the Spirit, with Muriel only revealing the existence of the Spirit Elemental when at the Pentagram as Darryl fit the bill perfectly and she therefore saw no need to look for one.
Book of ShadowsEdit
Once every century, the planets align in such a way that it causes the winds to shift and the climate to change.
During that period, weather becomes unstable and the Earth begins to shake as the world falls out of balance.
On the Night of Aeolus, by the light of the full moon, the elements must come together to set everything in its proper place.
To do this, a Firestarter is charged with gathering other Elementals at the Circle of Gaea to perform the Ritual of the Guardians.