men of iron

Roy C. Lackey wrote: In URTH Sidero tells Sev how his (Sidero's) kind came to be. They started out as glorified spacesuits for the sailors, becoming, as more gadgetry and circuits were added, self-aware entities capable of independent action. They are hollow because they were originally designed to house human sailors. Because they are hollow they are lightweight. Sev calls them androids and realizes that that is what Jonas had once been (chapter VIII). When he carried Jonas from the Antechamber he was surprised at how lightweight he was and speculated that it was due to his metal parts being made of some lightweight alloy. Wrong. He was lightweight because the metal parts were hollow, and the metal parts were made of iron, if not literally at least metaphorically.

And Matthew Malthouse wrote: If one accepts that the simplest solution suffices then Jonas and Sidero can be taken to be entities of the same kind - ex-space armour. But the contrast between Sidero's strenght and Jonas' weakness is marked. That weaknes I'd ascribe to the failing of the human parts Jonas used to repair himself which leads me to wonder how such a repair could have been effected on a hollow body.