Moisés salvo das águas

Poussin painted this in Rome in 1647 for Jean Pointel, a Paris banker who bought from him steadily. His other great French patron, Paul Fréart de Chantelou, heard about it and complained that Pointel was getting the better pictures.

Poussin answered on 24 November 1647. He named the painting, the Moses found in the waters of the Nile that Monsieur Pointel has, and asked whether Chantelou really believed he had made it with more love than the others. He then went into the modes of ancient music, the idea that every subject carries its own key and that a painter has to pitch the whole work to it. That letter has been argued over ever since by anyone trying to explain how Poussin thought. The canvas entered the French royal collection in 1665.