There was a third tonsure, which disappeared during the Middle Ages.
In the years since Pope Paul VI largely abolished the tonsure, in 1972, the of shaving a portion of the head of clergy and monks has largely fallen out of practice. The style, which may have originated as a symbol of the crown of thorns Christ wore during the passion, was indicative of a religious lifestyle or observance for nearly 1,500 years. Today, while some religious communities still wear them, the common Catholic doesn’t know much about them.
In a recent video by Vox, Phil Edwards takes a look at the history behind tonsures. There were two well-known forms of tonsure — the Eastern or Byzantine, which involved shaving the entire head, and the Roman, which bared a circular portion of the scalp. With the help of historian Daniel McCarthy, Edwards explains the historical relevance of tonsures and highlights a specific Celtic tonsure that was outlawed, because it created internal discord and “came to represent the differences between the Roman Catholic and Celtic Catholic church.”
While there is very little evidence of what this third tonsure looked like, as there are few depictions of it in medieval art, it was long thought to consist of shaving a stripe across the top of the scalp from ear to ear. McCarthy theorizes that it was cut in a triangle. The triangle tonsure, if that’s what it really was, was eventually banned by Rome, in an effort to promote unity.