2032. The piered watt (fig. 590.) may be of any thickness, with piers generally of double that thickness, placed at regular distances, and seldom exceeding the wall in height, unless for ornament. These piers are generally made square in the plan; but they have been found to be less obstructive to the training of trees, when rounded at the angles (a); or angular (b), and either hollow, or effected by deviation (c). The same remark will apply to piers formed partly to support the wall, but principally, as in the gardens laid out by London and Wise, Bridgman, &c. for sheltering the fruit trees. Where training is not a leading object, a thin deep projection (d) is much stronger as a whole, than the clumsy square piers generally formed by routine practitioners.