The map of Middle Earth was inspired by some heavy hints that Tolkein left:
-constellation Orion is seen from Middle Earth [in LOTR];
-Middle Earth has a moon [in LOTR].
-Mordor represents someplace in the Balkan region [reported comment, 3rd-hand].
-Shire is in England, possibly Oxfordshire [reported comment, 3rd-hand].
It all fits fairly well if we lower sea level (which actually occurred during ice ages), and
extend the Scandanavian mountain range across the German Plain (which is pure fantasy).
I think Tolkein's historic model was a mixture of Vienna defending against the Turks,
plus earlier Europeans defending against the Magyars ~900 AD.
You can find out more about Peter Bird at http://element.ess.ucla.edu/