Las Meninas: Who Is Looking at Whom?

In Las Meninas, Velázquez painted himself into the picture: he stands before a great canvas, looking back at "us" — while in the mirror at the back of the room, the king and queen appear. And so viewer, sitter, painter, and the figures in the mirror shift layer over layer, and who is looking at whom, who is the true subject, became a riddle with no set answer, debated for more than three centuries.