The treatment of the elements of perspective and light in painting was of particular concern to 15th-century Florentine painters. Uccello was so obsessed with trying to achieve an appearance of perspective that, according to Giorgio Vasari, it disturbed his sleep. His solutions can be seen in his masterpiece set of three paintings, the Battle of San Romano, which is believed to have been completed by 1460. Piero della Francesca made systematic and scientific studies of both light and linear perspective, the results of which can be seen in his fresco cycle of "The History of the True Cross" in San Francesco, Arezzo.