 In this work he analyses the nature of painting and explores the elements of perspective, composition and colour.In 1438 he began to focus more on architecture and was encouraged by the Marchese Leonello d'Este of Ferrara, for whom he built a small triumphal arch to support an equestrian statue of Leonello's father.In 1447 he became the architectural advisor to Pope Nicholas V and was involved with several projects at the Vatican.