Tropitae (τροπίται) were a sect of heretics who held that our Lord acquired a body of flesh by conversion of the substance of the godhead into the substance of flesh; an opinion which arose in the latter time of the Arian controversy among those who, maintaining the true divinity of the Son of God, and rightly desiring to maintain his sinlessness, were perplexed by the erroneous assumption that the human body, as such, is and cannot but be the seat of sin. To avoid the impiety of attributing a sinful body to our Lord, they devised the tenet that the body of Christ is consubstantial with his divinity, which passes into the somewhat more definite proposition that the substance of the Word is converted into the substance of flesh, and that the flesh being in the form of man is thus called human. This heresy was first dealt with by Athanasius (Epistle to Epictefus), A.D. 370. Apollinaris was at the head of those who denied the true incarnation of Christ, asserting the general proposition that the Son of God did not assume that which in man is the seat of sin; and varied applications of this proposition - were made by his followers.. A belief in the possibility of the conversion of the godhead into flesh almost necessarily presupposes the reception of the Cabalistic doctrine that all matter is an emanation from God. Athanasius remarks that Valentinus fancied the flesh to be a part of Deity, and so concluded that the passion was common to the whole Trinity. Fabricius remarks that the heresy is confuted by Tertullian. T-he Council of Chalcedon determined that the two natures in Christ are united ἀτρέπτως.