A Wat may contain just some of these structures or all of them. The most essential is the Bot, also called Ubosot. In general, with the exception of the Bot or of the Vihara, whose plan is conceived as a single unity within its enclosing gallery, the rest of the monuments are added little by little without special consideration of the general planning. But because of the contrasting forms of the large Bot or Vihara and the slender pinnacle of the Stupas or the solid vertical mass of the Phra Prangs, the resulting effect is always harmonious.