Optical illusions have been used since ancient Greece, when temples were designed with slanted rooftops and swelling columns to create the illusion that the structures appeared straighter and more proportional than they actually were. There are several types of optical illusions including ambiguous illusions that can be interpreted in multiple ways, distorting illusions that warp size or length, and physiological illusions involving afterimages. Optical illusions are a common part of daily life seen in technology like television and computers. A famous example is an illusion that made a downhill road appear uphill, tricking observers into thinking cars were being pushed uphill by the spirits of children killed in a crash.