A certain white stone, taken by Columba from the river Ness, near what is now the town of Inverness, had the singular power of becoming invisible, when the illness of the person requiring it would prove fatal. The selection of this stone was made in connection with the saint's visit to the court of Brude, king of the Picts, about the year 563. Adamnan, who tells the story, thus describes an interview between Columba and Brochan (the king's chief Druid or Magus), concerning the liberation of a female slave belonging to the latter: "The venerable man, from motives of humanity, besought Brochan the Druid to liberate a certain Irish female captive, a request which Brochan harshly and obstinately refused to grant. The saint then spoke to him as follows:--'Know, O Brochan, know, that if you refuse to set this captive free, as I advise you, you shall die before I return from this province.' Having said this in presence of Brude the king, he departed from the royal palace, and proceeded to the river Nesa, from which he took a white pebble, and, showing it to his companions, said to them:--'Behold this white pebble, by which God will effect the cure of many diseases.' Having thus spoken, he added, 'Brochan is punished grievously at this moment, for an angel sent from heaven, striking him severely, has broken in pieces the glass cup which he held in his hands, and from which he was in the act of drinking, and he himself is left half-dead.'" Messengers were sent by the king to announce the illness of Brochan, and to ask Columba to cure him. Adamnan continues:--"Having heard these words of the messengers, Saint Columba sent two of his companions to the king with the pebble which he had blessed, and said to them:--'If Brochan shall first promise to free his captive, immerse this little stone in water, and let him drink from it; but if he refuse to liberate her, he will that instant die.' The two persons sent by the saint proceeded to the palace, and announced the words of the holy man to the king and to Brochan, an announcement which filled them with such fear that he immediately liberated the captive and delivered her to the saint's messengers. The stone was then immersed in water, and, in a wonderful manner and contrary to the laws of nature, it floated on the water like a nut or an apple, nor could it be submerged. Brochan drank from the stone as it floated on the water, and instantly recovered his perfect health and soundness of body." The wonderful pebble was kept by King Brude among his treasures. On the day of the king's death, it remained true to itself, for, when its aid was sought, it could nowhere be found.