Summary Duke Karl (later King Karl XIII) was an active freemason and the founder of several quasi‐masonic orders. During the 1790s he had fitted out in his apartments at Stockholm Palace a small room which, judging by the painted decorations still extant, was clearly meant to be used for lodge meetings in one of these parallel orders. The room was designed by the artist Louis Masreliez, who also produced the full‐scale oudine drawings directly employed by the painter. Masreliez's sketches, drawings and full‐scale drawings, together with the building accounts, are now incorported in various archives and museum collections. Between them they convey an almost unique picture of the evolution of this late Gustavian interior design. What the archive materials do not shed light on is the very close co‐operation which must have occurred between Duke Karl and the artist, because the meanings of the painted decorations correspond to recondite structures of ideas peculiar to the various orders. We have cause to view the iconology of these paintings in direct relation to Duke Karl, as the person commissioning the decorations, the main personality involved and, probably, the author of the whole programme. When the room was redecorated, its one and only window was blocked up and a lantern roof substituted, with a decorated light shaft and ceiling. All that remains of these decorations is the painted ceiling, the centre of which is occupied by a gilded sun with a standing black griffin silhouetted against it. The griffin was emblazoned on Duke Karl's coat of arms, and without any doubt this emblem represents the main personality of the room, though not only as Duke of Södermanland but also as the leader of the secret order for which the room was furnished. The vigilance of the griffin is relatable to the corresponding qualities required of the rulers of a masonic lodge. The painting in the east probably represents a vacatio i.e. the mystic state of a human being when the spirit, released from its corporeal prison, is thereby enabled to behold the divine light. The 18th century brought a resurgence of interest in this manifestation of Neo‐Platonic mysticism, not least through the activities of Emanuel Swedenborg, and there is probably a close connection here with at least some of the new departures of freemasonry during the second half of that century. The “work” of the masonic lodge was in a certain sense a cultural activity and in another sense a speculative quest for mystic truths by many different paths. The themes of the four paintings undoubtedly include a reference to the points of the compass. If the eastern one may be presumed the last of the sequence, then the western one, at the point of the compass where the masonic pilgrimage towards the light began, is taken to be an allegorical depiction of a lodge where true knowledge is revealed. Iconographically familiar figures mingle with others which, it is clear, are directly connected with the structure of ideas within the order. The main character, at whose breast Minerva is pointing, or which indeed she may be embracing, symbolises friendship (i.e. the bonds uniting the brethren and sisters of the order) and at the same time the actual lodge or the new “earth”—the ideal community which the activities of the lodge were intended to establish. The borderline between a spiritual community and a physical ideal state is hard to distinguish. The goal of the activity appears to hover above the main scene in the form of a female figure, an idealised Mother Earth, delineated in light and holding, similarly depicted, a serpent and a pyramid. Beneath the main scene, Mother Svea is waiting for Duke Karl, the regent, to have gained the knowledge which will enable him to come forward as the ideal ruler. In the north and south, the contest between goodness and evil is in progress, the pilgrimage has begun and success is gained with the aid of the bonds of friendship within the lodge—the new life. In the north, the earth is tormented by evil and the innocent man seeks protection, while in the south the inward strength of the lodge is portrayed as the prerequisite for overcoming evil. The allegorical main figure, with her bared breasts can be interpreted as the perfected lodge or the new earth; in other words, this figure is the more perfect version of the one who in the western painting is gaining true knowledge. In the framework surrounding the four paintings, the person of the Duke is there for all to see. The ducal crown, the monogram and the griffin are reiterated and surrounded by allegorical figures which are more or less identifiable. And the whole thing is held together by a floral garland all the way round the ceiling—an allusion to the masonic bonds of union; another example of this occurs in the southern painting. Masreliez was able to use iconographic manuals for a certain part of these compositions; quite certainly, Ripa was consulted. The artist was among the most cultivated of his generation and the foremost exponent in Sweden of Neo‐Classical pictorial art. But Duke Karl was also highly erudite in this field, thanks to his thoroughly royal education, his intense personal interest and, not least, his very close involvement in freemasonry, the intellectual constructions of which were expressed with the aid of hieroglyphs. The masonic brethren, if anybody, were familiar with the usefulness and use of symbols—a fact which is too often underrated. The beautiful and at the same time closely packed decorations of Duke Karl's Cabinet provide, even though the rest of the interior decorations have vanished, a dramatic entrance to a world of ideas, depicted here, both intellectually and emotionally, in an artistic form which is still capable, to no mean extent, of adding to our understanding of the art and architecture of the 18th and 19th centuries.