In fact, the entire graduation ceremony is derived from the investiture ceremony from priests. Caps and gowns were originally the actual daily clothing worn in schools (most were in cold stone buildings, and so they were needed to stay warm). They were patterned on priests’ robes, since every major university in Europe that dates to that time originally was founded by a seminary associated with a cathedral. The granting of the diploma also came with the granting of a ring, just like a bishop. Originally, this was a sign of authority, and it contained the person’s seal for sealing documents in wax. For students, it was a visible sign of their expertise in a subject. This tradition also continues with the class ring. In fact, if you travel to some places in the Middle East today, people will still kiss your class ring if you go into a store or public place, just like people would kiss the ring of a bishop, as a sign of respect for your position and achievement. (I had this happen to me a couple of times in markets in Morocco, for example.)