When a ship is at sea under a full spread of canvas, there is an enormous force exerted on the masts. They would not be able to withstand without bracing in the form of ropes that run down to the deck. I have already described how the stays run between the masts and to the bowspirit and the jibboom, that take care of fore and aft forces applied towards he stern. Lateral rigidity is imparted chiefly by the shrouds and to some extent by the backstays. These latter pass slightly aft of the masts to the bulwarks and brace them in a fore and aft direction, thus taking care of forces imposed from astern.