The Cathars were also known as the Albigensians because they were centered around the town of Albi in Southwest France. Here the historian Will Durant writes about them in his 1950 book The Age of Faith
For some time the Cathari [a variant of Albigensianism] received a broad toleration from the ecclesiastics and the secular powers of southern France. Apparently the people were allowed to choose freely between the old religion and the new. Public debates were held between Catholic and Catharist theologians; one such took place at Carcassonne in the presence of a papal legate and King Pedro II of Aragon (1204). In 1167 various branches of the Cathari held a council of their clergy, attended by representatives from several countries; it discussed and regulated Catharist doctrine, discipline, and administration, and adjourned without having been disturbed . . .
. . . the nobles, relatively poor, began to seize Church property. In 1171 Roger II, Viscount of Béziers, sacked an abbey, threw the bishop of Albi into prison, and set a heretic to guard him. When the monks of Allet chose an abbot unsatisfactory to the Viscount, he burned the monastery and jailed the abbot; when the latter died the merry Viscount installed his corpse in the pulpit and persuaded the monks to choose a pleasing substitute. Raymond Roger, Count of Foix, drove abbot and monks from the abbey of Pamiers; his horses ate oats from the altar; his soldiers used the arms and legs of the crucifixes as pestles to grind grain, and practised their marksmanship upon the image of Christ. Count Raymond VI of Toulouse destroyed several churches, persecuted the monks of Moissac, and was excommunicated (1196) . . .
Innocent III, coming to the papacy in 1198, saw in these developments a threat to both Church and state. He recognized some excuse for criticism of the Church, but he felt that he could hardly remain idle when the great ecclesiastical organization for which he had such lofty plans and hopes, and which seemed to him the chief bulwark against human violence, social chaos, and royal iniquity, was attacked in its very foundations, robbed of its possessions and dignity, and mocked with blasphemous travesties.
(The Age of Faith, New York: Simon & Schuster, 1950, 772-773)
From Kenneth Scott Latourette [Baptist]: A History of Christianity: vol. 1: Beginnings to 1500 (NY: Harper & Row, 1953, 454-455):
The Cathari were dualists, believing that there are two eternal powers, the one good and the other evil, that the visible world is the creation of the evil power, and that the spiritual world is the work of the good power . . .
Some put forth a variant of this dualism, saying that the good God had two sons, one of whom, Satanal, rebelled, and the other, Christ, became the redeemer . . .
They held that since flesh is evil, Christ could not have had a real body or have died a real death . . .
From The Oxford Dictionary of the Christian Church [Anglican] (ed. F.L. Cross, 2nd ed., ed. F.L. Cross & E.A. Livingstone, Oxford Univ. Press, 1983, "Albigenses," 31):
. . . Their doctrine in its purest form was strongly dualist, akin to the Manichaean beliefs, and they rejected the flesh and material creation as evil . . . [they taught that] Christ was an angel with a phantom body who, consequently, did not suffer or rise again, and whose redemptive work consisted only in teaching man the true (i.e., Albigensian) doctrine.
Rejecting the sacraments, the doctrines of hell, purgatory, and the resurrection of the body, and believing that all matter was bad, their moral doctrine was of extreme rigorism, condemning marriage, the use of meat, milk, eggs, and other animal produce . . .