My Cat is Everything

Theory: Nobody who writes a physics textbook gives any fucks

Update: Legolas’ pupils are about 3.5 cm wide each. Now drawing kawaii Legolas on physics assignment.

Legolas’s pupil size isn’t the problem here, though. 5 leagues is 17.262 miles. The curvature of the Earth means that for a person of average height, the visual horizon is less than three miles away. Even if your vision is telescopic and the atmosphere is perfectly clear, you can’t see around the planet. If they were standing on a hill, it would have to be at LEAST 198 feet above sea level in order to see the horizon at 17.2 miles away, with nothing tall in between. Which, knowing Rohan, isn’t impossible.

you mean like

I shall never find peace.

Yeah there is.  The Silmarillion states that the world was curved after the fall of Numenor (I believe), preventing access to Valinor.  But Elves (among others) can travel the straight path across it.