But when the same Magnus, who now arrived at man's estate, had reigned for several years with equal energy and success, and all supposed that they had made sufficient provision against the storms of usurpation, the malice of the devil stirred up the priest aforesaid, as his proper engine, to disquiet the peace of this Christian people.
[...]Sverre (priest) then had recourse to witchcraft. He had in his retinue a certain daughter of the devil, powerful in witchcraft, and deservedly to be compared to her of former times, of whom the noble poet observes, that
The witch pretends that by her potent verse
Some souls are freed, while others feel the curse,
Just as she pleases; that her art has force
To stop the stars or rivers in their course --
To conjure nightly phantoms; when she wills,
Earth roars beneath, and trees descend the hills. [Virgil, Aeneid, 4:487ff]
At length this witch (as it is reported), with astonishing confidence in her destructive art, asked of her protecting usurper in what manner he would wish the enemies, which were before him, should perish. On his making choice that she should drown them, immediately, by the operation of the devil (who, indeed, by the power of his angelic nature has most influence over earthly elements when permitted by a superior power), the calm sea opened her mouth, and, in the sight of the enemy, swallowed up the greater portion of the royal fleet. On seeing this, the abandoned priest said, "Behold, my companions, how effectually the elements fight for us; be careful lest, perchance, those escape whose certain destruction the sea has left for your valor, that she may not seem to have done all." Wherefore the residue of the royal army, confounded at the sudden destruction of their associates, was easily overpowered, and the king himself killed.
On his death the affrighted kingdom submitted to tyrannical usurpation.