Not the untranslated Latin stymied me, but also the unfamiliar English words:
sumpter, limacine, intercalated, holt, vatic
flinders,costrel, mazar, carnet, cottars, cenada
felly, marcescent, rindles, theriac, carcalla
You may know these words, but I do not, and I had to look them up, often via search on the computer.

Most of these words are used only once in the entire novel and were not required for the furtherance of the story, but for a sense of the 14th century itself.  I get it, that the author wants to use words authentic to time and place, but when there are this many words in the first half of the book that a literate reader does not know and must hunt down in a dictionary, then the author is not writing for his readership, but for himself.

The author seems not to have heard of the use of apposite phrases to clarify the meaning of a word that may be unfamiliar to readers except for those who are experts in the field.  A professional historian, Barbara Tuchman in "A Distant Mirror" (history of the same century), does not find it necessary to use such specialized terminology for the most part, and when she does, she gives a brief equivalency in the same sentence or paragraph.

Furthermore, the author uses some words incorrectly--for instance, "resolving their climb", "chancery", "a swelter rose in his face". I found a word that was used at the time in Scotland and similar northern lands, not in Naples and Rome.  I seriously doubt that a church would have a crucifix on the outside--more likely a cross, for religious reasons not germane to this review.

It is very difficult to stay with the story when the words keep getting in the way; between the Latin, when untranslated, and the archaic English, the first half was very difficult to read.

The second half of the book seemed almost as though it had been written by someone else, chapter after chapter descriptive of the circles of hell, the tortures of the damned and the final confrontation.  Much easier to read, less untranslated Latin, fewer archaic terms.  I personally was uncomfortable with the sermons and lectures on various religious topics; your mileage may vary.
Not the untranslated Latin stymied me, but also the unfamiliar English words:
sumpter, limacine, intercalated, holt, vatic
flinders,costrel, mazar, carnet, cottars, cenada
felly, marcescent, rindles, theriac, carcalla
You may know these words, but I do not, and I had to look them up, often via search on the computer. Most of these words are used only once in the entire novel and were not required for the furtherance of the story, but for a sense of the 14th century itself. I get it, that the author wants to use words authentic to time and place, but when there are this many words in the first half of the book that a literate reader does not know and must hunt down in a dictionary, then the author is not writing for his readership, but for himself. The author seems not to have heard of the use of apposite phrases to clarify the meaning of a word that may be unfamiliar to readers except for those who are experts in the field. A professional historian, Barbara Tuchman in "A Distant Mirror" (history of the same century), does not find it necessary to use such specialized terminology for the most part, and when she does, she gives a brief equivalency in the same sentence or paragraph. Furthermore, the author uses some words incorrectly--for instance, "resolving their climb", "chancery", "a swelter rose in his face". I found a word that was used at the time in Scotland and similar northern lands, not in Naples and Rome. I seriously doubt that a church would have a crucifix on the outside--more likely a cross, for religious reasons not germane to this review. It is very difficult to stay with the story when the words keep getting in the way; between the Latin, when untranslated, and the archaic English, the first half was very difficult to read. The second half of the book seemed almost as though it had been written by someone else, chapter after chapter descriptive of the circles of hell, the tortures of the damned and the final confrontation. Much easier to read, less untranslated Latin, fewer archaic terms. I personally was uncomfortable with the sermons and lectures on various religious topics; your mileage may vary.