Shrine of Asuryan

The Shrine of Asuryan, an annual destination of the Phoenix King, is located on the Island of Flame due north of Lothern. Within this ancient pyramid's central chamber burns the eternal fire of the phoenix. When a new king is crowned, he bathes in these white-hot flames, passing miraculously unscathed through the inferno before emerging to be clad in ceremonial robes and the great feathered cloak of kingship. Both these ceremonies are overseen by the Phoenix Guard, the silent sentinels of Asuryan. Just as they attend the king on his journey to the flame, so too do they bear his lifeless body to the funerary White Ship when his mortal existence finally ends.

Source

 * Warhammer Armies: High Elves (8th Edition) -- pg. 11