into: _Primary_, or Thirteenth Century style; _Secondary_, or Fourteenth Century, often called _Rayonnant_ from the wheel tracery of the rose windows; _Tertiary_, or Fifteenth Century, called _Flamboyant_ from the flame-like shapes of the window spaces. On the other hand, in England, the divisions are: Thirteenth century or _Early English_; Fourteenth century or _Decorated_, because of the increased elaboration both of window tracery and rib vaultings; Fifteenth century or _Perpendicular_, owing to the predominance of vertical members in the tracery of the windows. The chief fountain-source of the early Gothic development was the Ile de France, whence the new ideas were carried, largely by monastic activity and especially that of the Cistercian order, to England, Germany, Italy, and Spain. In each of these countries their application was coloured by local conditions and England in particular produced a series of buildings, characterised by originality of treatment and grandeur of design. Nevertheless, it is recognised that French Gothic is pre-eminent, not only for the logic and skill with which structural problems were solved but also for sublimity of design, especially in the interiors, and for the sense of proportion that distinguishes the best examples. English Gothic, however, is a noble second. Before enumerating some of the famous examples of French Gothic, we may summarise the principles and devices more or less common to all Gothic. Romanesque had substituted equilibrium in place of the inert stability of the Roman architecture. The thirteenth century architects added to equilibrium _elasticity_. They achieved this by a development of the concentration of strains, which the Romans had invented or applied in the support of groin-vaulting on four piers, and the Romanesque architects had further developed by the system of rib-vaulting. =Pointed Arch.=--The Gothic was structurally evolved out of the rib vaulting and the pointed arch. In the first place, while the Romanesque architects used the rib system solely as a convenience of building, the architects of the Ile de France, adopting it for the same purpose, became conscious of its further possibilities in the direction both of construction and of beauty. The rib, no longer a crude arch of masonry, was constructed of mouldings that made it a feature of beauty, enhanced by the increased height and the finer sweep of line that the skill and taste of the French architects achieved.