Circle of Light

The Circle of Light is a holy place in Yew which could be found during the time of Ultima III.

Description
A sacred site of the city's druids, the Circle of Light is a unique structure made of rings of flame and water, with four clerics forever watching over it. It was rumored to be a place where the pious would have wisdom imparted to them. When the company of the Stranger came upon it, an ernest prayer revealed to them the word "Evocare," the exhortation needed to pass the Great Earth Serpent, which then guarded the Isle of Fire.

After the founding of Britannia following Exodus' defeat, the Circle was seen in Yew no more.

Trivia

 * "Evocare" is a Latin word meaning "to summon."
 * In the manga adaptation of Ultima III, the Circle of Light is a megalithic circle similar to Stonehenge, at which a  moongate may be summoned by the acolytes which dwell there. Early in the story, the protagonists seek this service, hoping to gain passage to Death Gulch. During the summoning, however, the city is attacked by daemons and a mystic barrier is erected around the circle which proves to be the last stand against the siege as the heroes step through the gate.