I am scanning Ovid's metamorphoses. For the line "unus erat toto naturae vultus in orbe," I have - - | - - | - - | - ' ' | - ' ' | - x. There doesn't seem to be an obvious position for the principal caesura in either the third or fourth foot (toto naturae - - | - ' ' ). Suggestions?
Incidentally, this line stuck out to me because of the coincidence of natural stress accents with the thesis of every foot of the hexameter.