Espalier is the horticultural technique of training trees through pruning an grafting in order to create formal "two-dimensional" or single plane patterns by the branches of the tree. The technique was popular in the Middle Ages in Europe to produce fruit inside the walls of a typical castle courtyard without interfering with the open space, and to decorate solid walls by such trees planted near them. Evidence exists suggesting that the technique dates back much further, perhaps even to ancient Egypt. The word espalier initially referred to the actual trellis on which the plant was trained to grow, but over time has come to be used to describe the technique.