Fidius
an ancient form of filius, occurs in the connection of Dius Fidius, or Medius fidius, that is, me Dius (Διός) filius, or the son of Zeus, that is, Hercules. Hence the expression medius fidius is equivalent to me Hercules, scil. juvet. (Cic. Fam. 5.21; Plin. Ep. 4.3.) Sometimes Fidius is used alone in the sense of the son of Zeus, or Hercules. (Ov. Fast. 6.213; comp. Varro, de L. L. 5.66; Plaut. Asin. 1.1. 8; Varro, apud Non. 8.93.) Some of the ancients connected fidius with fides. (Festus s. v. medius.)
From William Smith (ed.), Dictionary of Greek and Roman Biography and Mythology. Text provided under a CC BY-SA license by Perseus Digital Library, http://www.perseus.tufts.edu, with funding from the National Endowment for the Humanities and Tufts University. Data accessed from https://github.com/PerseusDL/canonical-pdlrefwk/ on 17 October 2026.