The Italian Renaissance artists used linear perspective to convey a sense of depth in their works. It is a mathematical understanding of a painting, which has to have a vanishing point - it is a point where all the lines, which constitute the vastness of the space, converge. Along the lines, we see the depth in the space. For example, if we are looking at a room, the objects closer to us, as viewers, would be bigger, and those that are far away would be smaller. We would be able to literally draw lines through the painting, which would intersect at a point - and that's what the Renaissance artists did, before even starting to paint.