In the eleventh century Bernard of Clairvaux (A.D. 1091-1153) and Hugo of S. Victor carry on the mystic tradition, with Richard of S. Victor in the following century, and S. Bonaventura the Seraphic Doctor, and the great S. Thomas Aquinas (A.D. 1227-1274) in the thirteenth. Thomas Aquinas dominates the Europe of the Middle Ages, by his force of character no less than by his learning and piety. He asserts "Revelation" as one source of knowledge, Scripture and tradition being the two channels in which it runs, and the influence, seen in his writings, of the Pseudo-Dionysius links him to the Neo-Platonists. The second source is Reason, and here the channels are the Platonic philosophy and the methods of Aristotle--the latter an alliance that did Christianity no good, for Aristotle became an obstacle to the advance of the higher thought, as was made manifest in the struggles of Giordano Bruno, the Pythagorean. Thomas Aquinas was canonised in A.D. 1323, and the great Dominican remains as a type of the union of theology and philosophy--the aim of his life. These belong to the great Church of western Europe, vindicating her claim to be regarded as the transmitter of the holy torch of mystic learning. Around her there also sprang up many sects, deemed heretical, yet containing true traditions of the sacred secret learning, the Cathari and many others, persecuted by a Church jealous of her authority, and fearing lest the holy pearls should pass into profane custody. In this century also S. Elizabeth of Hungary shines out with sweetness and purity, while Eckhart (A.D. 1260-1329) proves himself a worthy inheritor of the Alexandrian Schools. Eckhart taught that "The Godhead is the absolute Essence (Wesen), unknowable not only by man but also by Itself; It is darkness and absolute indeterminateness, _Nicht_ in contrast to _Icht_, or definite and knowable existence. Yet It is the potentiality of all things, and Its nature is, in a triadic process, to come to consciousness of Itself as the triune God. Creation is not a temporal act, but an eternal necessity, of the divine nature. I am as necessary to God, Eckhart is fond of saying, as God is necessary to me. In my knowledge and love God knows and loves Himself."[154]