Roman demigod, son of Mars and Rhea Silvia; twin of Romulus; killed by Romulus during the foundation. The fratricide-at-foundation episode is structurally central to Roman political imagination — Wiseman (1995) reads it as a 4th-c. BCE elaboration responding to plebeian-patrician class conflict. Distinct from the Heracles-and-Iphicles twinship in the registry: Romulus and Remus are both ½ demigods (same divine father, same mortal mother) where Iphicles is purely mortal — the Roman tradition makes both twins demigods because Mars's paternity covers both via the same divine encounter.