The eternal Flames of the Principles are besides the Book of Truth, the Candle of Love and the Bell of Courage, the most visible signs of the three principles in Britannia. Each of these flames is kept in the stronghold representing the principle.
The Flame of Truth is located in the Lycaeum on Verity Isle. The keeper of the flame was named in Ultima VI, although it is possible that Mariah herself had taken over this duty as the head of the Lycaeum.
The Flame of Love is located in Empath Abbey in north-western Britannia. Sionnach had taken over this duty.
The Flame of Courage is located in Serpent's Hold on the Isle of Deeds. The keeper of the flame in Ultima VI was Lady Tessa, as she told the Avatar when talking with her.