This is an old expression explaining what penalty faced those guilty of treason in England in the 12-1300's.
The convicts were hung (with a rope around the neck so that they could not breath) almost to the point of death, then drawn by horse ('drawn by horse' means that they were transported by a horse) and quartered means that their bodies were cut into four pieces.
Here is more information about the procedure: http://en.wikipedia.org/wiki/Hanged,..._and_quartered
It's very gruesome and gladly it doesn't happen today!
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