In Book VII of his Historia Naturalis, Pliny the Elder wrote of the "undead", including this one account of somebody with a peripatetic "soul":
"With reference to the soul of man, we find, among other instances, that the soul of Hermotinus of Clazomenae was in the habit of leaving his body, and wandering into distant countries, whence it brought back numerous accounts of various things, which could not have been obtained by any one but a person who was present. The body, in the meantime, was left apparently lifeless. At last, however, his enemies, the Cantharidae, as they were called, burned the body, so that the soul, on its return, was deprived of its sheath, as it were."
From a non-supernatural view of possible vampirism in ancient Rome... if Suetonius is to be entirely believed regarding the excesses of the Roman emperors, then it probably wouldn't be too far-fetched to imagine perhaps Tiberius or Caligula having indulged in blood-drinking fetishes.
-- Nephele