Vitruvius outlined three principles of design: utilitas (usefulness), firmitas (durability), and venustas (beauty). These principles were discussed in the document through examples of furniture and space design. Function, structure/durability, and aesthetics should all be considered for a well-designed object or space. An excellent design meets the intended use, will last appropriately, and has a pleasing appearance, while an unsatisfactory design fails to fulfill one or more of these principles.