In a comment Robbie wrote in the 060118 MMDigest:

>[ Margrave: the English equivalent of Margraf, the German hereditary
>[ title of nobility that originally meant a military lord or keeper
>[ of the borders.

It's correct, except for the spelling: the German word is Markgraf.
In Germany a Markgraf often is called a Marquis, which became Marquess
in English.

Originally a marquess indeed was supposed to defend the borders; it
was a military function.  Later on it became a more political purpose:
since a marquees was higher in rank, he could be used by a superior
(an earl) to supervise a group of dukes -- with military power when
necessary, of course.

The territory (the marquisate or marquisship) at that time no longer
was exclusively found at the borders.  Even later the title was
bestowed as a reward, with no specific (noble) function.

Jan Kijlstra