Where? When?
Another possible origin for the Cyclops legend is that prehistoric proto-elephant skulls were found by the Greeks (some still exist today on Crete). Due to the large central nasal cavity (for the trunk) in the skull, it might have been believed that this was a large, single, eye-socket. The smaller, actual, eye-sockets are on the sides and much less impressive. Given the paucity of experience that the locals likely had with living elephants, they were unlikely to recognize the skull for what it actually was.
and another: http://www.users.globalnet.co.uk/~loxias/odyssey/cyclops02.htm
There's a new book (Spring 2000) from Princeton University Press by Adrienne Mayor, which advances the theory that tales of Griffins, Giants and Centaurs as well as Cyclopes arose from interpretation of the fossil evidence by the ancients. It's called Palaeontology in Greek and Roman Times. The dwarf elephant theory to explain the Cyclops was first thought of in 1914 by Othenio Abel.
but I think this is the one I'm remembering: http://www.calacademy.org/exhibits/skulls/diversity.html
SKULL FACT
In the 14th century, Giovanni Boccaccio claimed he had discovered a mighty Cyclops skull inside a Sicilian cave. This one-eyed monster may have been nothing more than a docile elephant. The hole that resembles a central eye in the elephant’s skull is actually its nasal cavity – it is surrounded by plentiful muscle attachment space for the animal’s massive trunk.
That includes the middle ages reference and I took several science, anthropology and archaeology classes in the University of California system while I lived out there.