Line has been around for a long time. Ever since the prehistoric era, when that first artist picked up a lump of wood ash from a spent campfire and outlined a hand on the cave wall, lines have described forms of all types–human, animal, and landscape. On its own, line is a very powerful force. A line can depict the simple silhouette of a form as well as its more complicated interior dimensions. When used in a hatching manner, it can even simulate value. And when joined with softer, smudged tones known as value masses, you have a combined unstoppable force–except, perhaps, by a good eraser.