The Giant Puzzle of the Frescoes from the House of the Harpist, Arles
The House of the Harpist is a Roman villa on the banks of the Rhone in Arles, Frances. It was built between 70 and 50 BC, so before the town of Arles was founded as a colony for Caesar's veterans, and abandoned by 40 BC.
The site has long been known and there have been multiple campaigns of excavation. During the most recent dig, in 2014-2017, the archaeologists completely cleared two rooms. They discovered that the lowest level of fill in the rooms was composed almost entirely of small fragments of painted plaster from the walls. They collected 80 crates full of this material, enough for about 105 square meters of wall (1100 square feet).
The French government recently announced a campaign to study the fragments and reassemble them as fully as possible, which they estimate will take three years. Quiet a puzzle.