The Yale Alumni Magazine has an article by Angus Trumble in the latest issue called “Old hat: The evolution of your mortarboard,” which despite its focus on the mortarboard (a descendant, it turns out, of the pileus quadratus, the hot new fashion item of the early 16th century) has much to say about the history of hats in general; I particularly recommend the family tree, with its fetching portraits of everyone from popes to bellhops wearing the illustrated items. (Depending on your browser window, you may have to scroll a bit to the right to see the vertical line representing the crown, which—like the papal miter on the left—does not interact with the rest of the tree.)
Googling for more on the pileus quadratus, I found this gallery of religious headcoverings (in German), which I thought might interest you. (Second page here.)
Good lord, what a collection—many thanks! I was thinking “what’s that zucchetto doing in a saucepan?” until I realized it was just a specialized hatbox. And I was quite startled when I scrolled down and hit a string of homburgs after all that priestwear.
And the second page is even wilder!
I have been blogging our summer research trip to Europe, and found a wonderful advertisement for academic headcoverings on the wall at the University of Verona. Naturally, I thought of you immediately:
Italian graduation hats
I love it—thanks!