and gives the visual effect of having been flattened under pressure. Its structure is achieved by drafting two arcs that rise steeply from each springing point on a small radius and then turn into two arches with a wide radius and much lower springing point. This type of arch, when employed as a window opening, lends itself to very wide spaces, provided it is adequately supported by many narrow vertical shafts. These are often further braced by horizontal transoms. The overall effect produces a grid-like appearance of regular, delicate, rectangular forms with an emphasis on the perpendicular. It is also employed as a wall decoration in which arcade and window openings form part of the whole decorative surface. The style, known as Perpendicular, that evolved from this treatment is specific to England, although very similar to contemporary Spanish style in particular, and was employed to great effect through the 15th century and first half of the 16th as Renaissance styles were much slower to arrive in England than in Italy and France. It can be seen notably at the East End of Gloucester Cathedral where the East Window is said to be as large as a tennis court. There are three very famous royal chapels and one chapel-like Abbey which show the style at its most elaborate: King's College Chapel, Cambridge; St George's Chapel, Windsor; Henry VII's Chapel at Westminster Abbey and Bath Abbey. However, very many simpler buildings, especially churches built during the wool boom in East Anglia, are fine examples of the style. Tracery patterns Most 19th-century histories of Gothic architectural style used a series of typological categories based on the evolution of the dominant patterns of window tracery. In terms of the overall development of Gothic architecture, the crucial development was not so much the use of any particular tracery patterns but the transition from plate to bar tracery, which was what made the Rayonnant and subsequent styles possible. To construct traceries proportionately it is important to use the basis of geometry to help create correct angles for the design. Rounded quatrefoils In Gothic tracery, rounded quatrefoils have been used in modern industrial ornament which is used to embellish different parts of a building or certain objects. This is formed with the use of squares as the base and then constructing circles tangent to each side of the square in the center of the side as well