Privately printed, 1678 From the first printing of the most ambitious Spanish architectural treatise to date, a provocative work in which the author argues the superiority of ‘oblique’ archi­tecture to ‘straight’ (Vitruvian) architecture, and famously censures Bernini’s designs for the colonnade around St. Peter’s Square and staircase (Scala Regia) in the Vatican, and equestrian statue of the Emperor Constantine (the later spoilt, Caramuel argued, by the height at which it was placed). Caramuel’s obsession with geometry and optical distortion was treated as madness by some contemporaries; others, such as the architect and theoretician Guarino Guarini, ‘who carried on with Caramuel intensive discussions as he did with no other theorist’, took him very seriously. Intended for Spanish readers, the treatise had greatest impact in Catalonia and in the New World, where Caramuel’s ideas were spread by theologians and mathematicians, and examples of ‘architectura obliqua’ are numerous. The majority of the engravings are by anonymous printmakers: one print is signed by the Roman engraver Bernard Balliu (part 4, pl.6), five by the Milanese engraver Giovanni Francesco Bugatti (fl. 1670–1695),10 seven by Cesare Laurentio (fl. 1657–1689),11 and eleven by the Milanese printmaker Simone Durello (1641–1719). Of great scarcity, only 24 examples are known worldwide. Very light staining. Good overall condition.