Picasso began drawing in a new revolutionary way. He began playing with the spaces in each of his drawings in a new geometrical way. This new way of playing with the spaces was called cubism.He was one of the co-founders of this new movement. This different way of painting lead to what now we know as 3d images playing with the spaces that sorround somethig.
http://www.artchive.com/artchive/P/picasso_protocubism.html
http://maryadamart.com/Cubism_The_Big_Picture.htm