How does The Last Supper painting show realism?

The perspective in Leonardo's "The Last Supper" mural only makes sense from the opposite end of the Chapel. He elevated the entire "head table" of a banquet to the height of 12 feet, mimicking an extension of the Chapel to painted Windows at the far end. From the floor of the Chapel (which was then only the dining hall), the monks in this small monastery could only have looked up to wonder why the walls looked off-balance.

Because he used a new paint that was untested, it began falling apart during his own lifetime, and most of the painting has now been painted-over by "conservators".