Palladio would often model his villa elevations on Roman temple facades. The temple influence, often in a cruciform design, later became a trademark of his work. Palladian villas are usually built with three floors: a rusticated basement or ground floor, containing the service and minor rooms. Above this, the piano nobile accessed through a portico reached by a flight of external steps, containing the principal reception and bedrooms, and above it is a low mezzanine floor with secondary bedrooms and accommodation. The proportions of each room within the villa were calculated on simple mathematical ratios like 3:4 and 4:5, and the different rooms within the house were interrelated by these ratios. Earlier architects had used these formulas for balancing a single symmetrical facade; however, Palladio's designs related to the whole, usually square, villa.