Overview
Dante's Sixth Circle lies within Lower Hell, the region encompassed by the walls of Dis, that demarcation between sins of Incontinence and sins of Violence. His primary denizens here are The Heretics. They receive considerable attention in his text, with four separate Cantos (8 through 11) dedicated to them, more than any other group in The Inferno.
I found it necessary to keep my Sixth Circle above that division marked by the walls of Dis, because it is the final realm of Logical Fallacies, those that Fail to be Relevant. This Sixth realm lies between the Styx and the crumbling walls of the city, and consists of immense piles of rocky debris that shift about constantly.
Comments
The term heresy itself comes from the Greek word for "a choosing" and become synonymous with choosing anything other than orthodox Church doctrine. During Dante's era, the desire that every member of a community believe exactly as they were told was so strong, and the fear that a heretic would corrupt others was so overwhelming, that it was considered paramount to cut the offending body out of the picture as effectively as possible. Heretics were given a chance to recant their beliefs. Those that did not kowtow to such pressures were typically taken to the stake. The official pronouncement of Pope Innocent III (what an ill-fitting name) was: "Anyone who attempted to construe a personal view of god which conflicted with the church dogma must be burned without pity."
The hysterical concern with heresy was kicked off in the twelfth century, in reaction to the Cathars, or Albigensians, a sect that considered the world to be a creation of an evil being. They believed in reincarnation. Yet they were also Christians that spurned material wealth and considered Jesus to be the son of God. And as they openly despised the Catholic Church and labeled it as a tool of Satan, it isn't surprising that they incurred its wrath (though this hardly excuses the horrific executions that the Church sponsored and called for, and then had secular authorities carry out).
The Cathar persecutions reached their heights decades before Dante's birth. During his lifetime, a popular target of Catholic persecution was the Beguines, a loosely organized order of Christian women. These women held no particularly unorthodox beliefs, lived lives of voluntary simplicity, served the needy, accepted the Church and its authority, and attempted to provide translations of devotional documents that the laity could understand. Marguerite Porete, a Beguine who scandalously wrote (in French, and not in Latin) that it was possible for the soul to find union with God in this life and therefore not need to explicitly cultivate virtue, was rewarded with a trip to the stake in 1310.
And its nice to see that after the excruciating end that these people were given on earth, Dante's God provides them the bonus of eternal suffering in a like manner: his heretics are encased in burning tombs with red-hot walls. There's that love, intellect, and justice again, in this case all for a minor difference in the interpretation of dogmas that cannot be tested against reality.