What is a sagbut? a type of cello?

A sagbut, or sackbut, is a medieval instrument that most closely resembles the modern trobone. It was mostly used in the renaissance and baroque eras, and featured a slide which changed the pitch of the instrument due to the way it altered the length of the tube.

The answer is

Perspective is important because it enabled the 3 dimensional world to be translated into the 2d world of the picture plane. this had an immediate impact on the representation of reality in art and design.