In front of his palace in Kolomenskoye stood a long box, in which any person could put his or her complaint. Alexandre BenoisThere is another version, according to which the expression "to put in a long box" appeared in the middle of the 18th century. The complaints of those who were poorer were considered last, sending them to a... long box. So, perhaps, the expression migrated into the Russian language together with the habit of postponing everything insignificant for later. That's how the expression came to be, which means "to put something off for an indefinite period of time".