Once upon a time, Merlin was in a battle and had a vision that he would die a triple death that day. He asked St. Hentigurn to perform the sacrament (which I'm assuming is similiar to Christianity's Last Rites, a final blessing). Later that day he was seized by his enemies who beat him with stones and clubs and threw him in the river, then stabbed him with a wooden stake. Hence the triple death by beating, drowning and stabbing.

It is said he is buried at the root of a thorn tree in a field beside the village of Drumelzier near the River Tweed, in the south of Scotland.

A scottish prophet named Thomas the Rhymer made a prophecy about it;
"When Tweed and Powsail meet at Merlin's grave
Scotland and England, shall one Monarch have."
And it came true in 1603, when the river Tweed overflowed and met the Powsail river at the site of Merlin's Grave -- on the very same day that the crowns of Scotland and England were first united under James VI of Scotland (aka James I of England).

I vote that Mr. Bausch takes us on a field trip to go see it.
As long as it doesn't make Canada and America share a monarch too.