The vestals are the caretakers of the crystals.
There is a Vestal of the Wind Crystal in Ancheim, the Water Crystal in Florem, the Earth Crystal in Eternia, and the Fire Crystal.
While Bravely Default takes place, three of the four vestals are dead. The only living vestals when the game started were the vestals of wind and water. The vestal of water, Olivia was killed by Victoria during the game.