OK, despite what I'm about to say, I enjoyed watching the film. Nothing, however, is perfect, and this piece suffered from as much ignorance as I have seen in any attempt to recreate the early Middle Ages. I was a monk for many years, so maybe I know more about such things than I should. Still, it looked as if the producers were trying without knowing how to try.
For instance, when Patrick, upon his return from slavery, asked his father for "a Bible", he was asking the impossible. There was no such thing available. The most he could have gotten would have been a bound book of the 150 Psalms, or maybe--since his father was, as depicted, a patrician landowner--a book containing the four Gospels. The story omitted any mention of the fact that Patrick's father was, himself, a deacon in the Church.
Further, there was no "arduous course of studies" for the priesthood, and people didn't have to travel to Gaul for training and ordination, though some, indeed, did. Training and ordination normally would have been undertaken by the local bishop.
Then, when Patrick said to Bp Quentin, "In Matthew, the 16th chapter, verses 19 and 20...", that, too, was impossible. The Bible wasn't divided into chapters and verses until the 17th century, by Archbishop Ussher. What Patrick *should* have said would be more like "Remember the words of Our Lord which we read in the Gospel for the 2nd Sunday in Lent..." Oh, and the grammar of the quoted Biblical passages--pronouns and verbs all mixed up? Homer Simpson does just about as well. (It's not hard to look something up and copy it out right.)
By the way, Patrick was far from ignorant of Latin, as portrayed in the scene with Bp Quentin. He wrote Latin poetry, and his autobiography (as partly read in a later scene) was written in fairly decent Latin.
Now--the vestments. It looked as if the producers had raided all of the costume shops in Lower Manhattan, and a few of the church sacristies, and tossed together whatever looked good to them--none of it the least bit authentic.
Bishop Quentin's getup was the worst--a modern Byzantine chasuble and a 15th-century Venetian Doge's cap. The copes worn by the other bishops and Patrick were of 18th-century design, which persisted down to fairly recently, when the flaps on the back began to be restored as proper hoods--and these were topped off in the film with 16th-century Canterbury caps! The white surplices worn by the messengers and acolytes and the white albs worn by the slaughtered flock of newly-baptized came right off the shelf of Guardian Church Goods on 7th Street. Pfui.
As I said, enjoyable enough, but it could have been way better if the producers had simply asked me!
