“Let all men know how empty and worthless is the power of kings. For there is none worthy of the name but God, whom heaven, earth and sea obey”.
So spoke King Canute the Great, the legend says, seated on his throne on the seashore, waves lapping round his feet. Canute had learned that his flattering courtiers claimed he was “So great, he could command the tides of the sea to go back”. Now Canute was not only a religious man, but also a clever politician. He knew his limitations – even if his courtiers did not – so he had his throne carried to the seashore and sat on it as the tide came in, commanding the waves to advance no further. When they didn’t, he had made his point that, though the deeds of kings might appear ‘great’ in the minds of men, they were as nothing in the face of God’s power.
Excerpt from http://viking.no/e/people/e-knud.htm