It’s the time of year when jigsaw puzzles, in a variety of subjects, sizes and complexity are popular gifts among families.

Engraver and cartographer John Spilsbury is credited with making the first jigsaw puzzles in 1760. He mounted maps of Europe on a wood backing, cut around the national boundaries and called them “Dissected Maps”.

The Ghent Altarpiece can be likened to a “disected map”. It has 24 pieces which fit together front and back, akin to a double-sided “jigsaw”. Simple enough. What is more testing, and has been for six centuries, is piecing together the iconography in each panel.

The Just Judges panel is probably the most complex, but if viewed as individual jigsaw pieces it starts to make sense. Each piece (or rider) has four interlocking attributes to allow four other pieces to fit. If only one attribute fits and not the others, then a wrong identification is the result. It’s Van Eyck’s way of confirming the identity of the riders. The puzzle can also be likened to a visual crossword. The clues are cryptic and often a play on words.

Coincidently, the Ghent Altarpiece, particularly the Just Judges panel, also highlights locations and national boundaries. Then there are the more obvious boundary references: heaven and earth, life and death.