To harry someone to the point of mad desperation. The image here is forcing a person to escape a pest by literally climbing up and over a wall. An earlier version was to drive to the wall, the wall being as far as one could go to escape. It dates from the sixteenth century. “I am in this matter euen at the harde walle, and se not how to go further,” wrote Sir Thomas More (1557). The current cliché dates from the twentieth century, and probably comes from the behavior of an addict deprived of drugs or alcohol who actually tries to climb the walls of a room or cell in desperation (see also drive to drink). However, it is most often used to express exasperation at being “driven crazy”: “‘Mad as a hatter,’ said Gillian Soames complacently. ‘Stark raving bonkers. Up the wall. Round the twist’” (Robert Barnard, Death and the Chaste Apprentice, 1989).