I don't know if Italian sedere or Romanian`s equivalent shifted semantically.
That's actually an easy one. Rulers sit, subjects stand. Those who are allowed to sit are noble, and their behavior defines propriety. A judge who is in office is said to be a sitting judge. A monarch is said to be on the throne. The pope issues encyclicals ex cathedra 'from the chair'. – jlawler Jul 23 at 20:45