Serlio helped canonize the classical orders of architecture in his influential treatise variously known as 'I sette libri dell'architettura' (Seven books of architecture) or 'Tutte l'opere d'architettura et prospetiva' (All the works on architecture and perspective). By 1537, when the earliest of his books was published, Serlio had been working on the treatise for at least a decade and had already organized it as a work in seven books. Although Serlio completed all seven projected books, only the first five books were published during his lifetime. The sixth remained in manuscript until the 20th century