> As far as I know, the full weight of topos theory isn’t even needed for algebraic geometry The original topos theory developed by Grothendieck and his collab

> As far as I know, the full weight of topos theory isn’t even needed for algebraic geometry The original topos theory developed by Grothendieck and his collaborators in the 60s is quite pragmatic and served to define cohomology theories for varieties over finite fields. Later other people, coming from mathematical logic, distilled "elementary" axioms from there and developed another kind of topos theory that is pretty much divorced from algebraic geometry.