There is a strange and mysterious subject amid the drawings of weapons and mechanisms for civil machinery in Manuscript B: an interlocking cube. The drawing clearly lacks a context and occupies space left free by previous drawings.

The typical Leonardesque lines and shading define a finished object. This is no sketch, and it has nothing to do with the other mechanisms on the page. It’s an axonometric drawing of a cube with lines dividing it into eight corners plus an identical figure in the center of each side.

What is it? Leonardo never drew anything like this in any other manuscript. It’s a small, simple and fascinating three-dimensional object. The central interlocking shape was surely inspired by a previous drawing on the right-hand folio: a system of interlocking bulkheads for building seafront structures. The shape of the posts provided the material for this subject. The eight corner pieces are formed so as to hold the central face of each side in position. Once all eight corner pieces are secured around the central body, the structure is solid and locked in place. If just two of these corner pieces were missing, we could easily open the whole thing by proceeding to remove the centers of each side.

For this reason, this could be either a small interlocking game or a little strongbox that can only be opened by someone who knows the interlocking sequence.