An unknown manuscript in the Koninklijke Bibliotheek (Royal Library) of Brussels (ms. II 7617) by the Bruges mason/bricklayer Charles De Beste: Architectura. Dat is Constelicke Bouwijnghen huijt die Antijcken Ende Modernen of 1599 forms a significant addition to our knowledge of Vitruvianism and Dutch theory of architecture in the sixteenth century. The work is not a translation of De Architectura Libri Decem, but on the basis of sixteenth-century commentaries on Vitruvius and followers it deals with a diversity of subjects from classical and contemporary architecture. Occasionally the texts are supplemented with De Beste's own, sometimes critical, observations and references to the situation in the Netherlands in general and in Bruges in particular. De Beste's treatise on architecture consists of eight books, devoted to arithmetics, geometry, astronomical instruments, sundials, architecture, perspective, fortress-building and artillery, respectively. At times the contents and illustrations of De Beste's treatise, dedicated to interested devotees of architecture, are quite close to contemporary northern building practice, whereas in other cases they are relatively theoretical in character and based on outdated examples. The variety in contents of the themes and the size of the manuscript, comprising a total of 578 folios, are a clear indication that the usual interpretations of the reception of Vitruvius and his commentators in Dutch sixteenth-century theory of architecture are no longer tenable. In these interpretations, mainly based on the printed documents of Coecke van Aelst and Vredeman de Vries, Dutch translations and commentaries are one-sidedly explained as practical examples for craftsmen for the application of colonnades and ornaments. Although Pieter Coecke van Aelst and Hans Vredeman de Vries dedicated their well-known treatises on architecture to craftsmen, these works - as the author puts it - were first and foremost meant for the group of art-loving enthusiasts and commissioners to whom De Beste ...