The oldest surviving treatise on architecture is Vitruivius' highly influential de Architectura. Marcus Vitruvius Pollio (born c. 80–70 BC, died after c. 15 BC) was an engineer of war machines, and skilled enough that he received a pension from the emperor in his retiurement, conditional on his writing a book that put forward his ideas about engineering and building. Of note is that he defines two forms of intelligence, contrasting the engineer with the architect: Rationalis describes the rationality and problem-solving capability of the engineer, whilst Sollertia is a form of cunning or mischief that he recognizes in architects, in particular, in the section devoted to (his) war machines, he remarks that the architects of a besieged town diverted the aqueducts into the fields in front of the city walls, turning them into a quagmire and preventing the approach of the besieging ballistas. Clearly Vitruvius has the greatest respect for this kind of ingenuity, as it is capable of entirely unfounding all of the fastidious technicity of the engineer. Of note, also, is that Vitruvius outlines a relational design aptitude that, in the case of ballistae, combines complex mathematics that calculate the trajectory of a given mass, and relate it to the diameter of a sinew braided from womens' hair: the entire machine then developed relationally from the proportions of the holes established for the braids. Likewise there is no fixed model of a temple (or any other building), but rather the necessary relationships that will result in a structural and elegant final form. Once again sollertia and parametric intellect seem at play as we negotiate a new architecture-of-mind native to a now-digital apparatus.