When a sage is approaching, one should rise up before he gets within
four ells' distance, and remain standing until he has gone as far past.
When a chief magistrate is about to pass, one must rise as soon as he
comes in sight, and not resume the seat until he has passed four ells.
When a prince passes, one must stand up whenever he appears, and not sit
down again until the prince himself is seated; for it is said (Exod.
xxxiii, 8), "All the people rose up, ... and looked after Moses until he
was gone into the tabernacle."
THE TALMUD, _Kiddushin_, fol. 33, col. 2.