So-called Gothic architecture was no spontaneous and miraculous manifestation. Like all human activities, its end is easy to determine; but it is difficult to fix even an approximate date for its beginning. The traces of its origin are lost in that period of architectural activity which preceded it, and prepared its way by a train of unbroken evolution. The cupola of St. Front, which we may reasonably call the mother cupola of France, was not an imitation of that of St. Mark at Venice, for both were based upon the church built by Justinian at Constantinople, in honour of the Holy Apostles. But the form thus imported into Aquitaine received such modification and development, as to make it virtually an original achievement. One of the knottiest of architectural problems was solved in the process, and that admirable constructive principle was established which consists in concentrating the thrust of a vault upon four points of support strengthened by pendentives. The construction of such a cupola as that of St. Front in dressed stone was an event of great moment in a district which still preserved the Gallo-Roman tradition in its integrity, and was commonly reputed the fatherland of our architecture. Its immediate consequences were shown before the close of the eleventh century by the erection of large abbey churches on the model of St. Front in various neighbouring provinces. But while accepting the new principle, the architects of the period directed their energies to its perfectibility. Their efforts, and even their successes, in this direction are manifest so early as the first years of the twelfth century. The churches of Angoulême and of Fontevrault may be cited in proof. "We here recognise the main preoccupation of the Romanesque builders--namely, how best to reduce the immense masses of churches built with the primitive cupola by a more deliberate and judicious distribution of thrust and resistance. We further see how the adoption of these principles led to the emphasising of critical points by buttresses, which now began to project from the exterior walls."[3] [3] _L'Architecture Romane_, by Ed. Corroyer; Quantin, Paris, 1888. The new system spread rapidly, notably in Anjou and Maine, its growth being marked by an ever-increasing refinement and perfection. The architects of the rich abbeys of these provinces, the importance of which was aggrandised by their strong attachments to the all-powerful religious organisation of the period, gave a further development to the Aquitainian method. They transformed the pendentives of the cupolas into independent arches which performed exactly the same functions, thus logically working out an architectonic principle of amazing simplicity, the success of which was so rapid that, by the middle of the twelfth century, it was systematically applied to the construction of great churches at Angers, Laval, and Poitiers.