What’s the origin of commencement mortarboards?

Pat Greenhouse/Globe Staff/Globe Staff

It’s commencement season in Boston, a city that boasts almost 30 colleges and universities. On any given weekend, you’re almost as likely to catch a glimpse of someone wearing a cap and gown as you are to see a fan in a Red Sox hat.

But the caps and gowns worn by graduates have a much longer history. In recent decades, caps even have become space for graduates to express their individuality.

The tradition of the cap and gown has persisted since the Middle Ages, when universities were founded by churches — students were clerics and required to wear academic gowns at all times. The hooded swath of fabric kept academics warm in unheated stone buildings.

The cap we know today, which resembles a skull cap with a square board perched on top, is thought to have evolved from a tufted, square cap (called a pileus quadratus) worn by medieval laity. The term for the modern cap, mortarboard, stems from its resemblance to a mason’s square board for carrying mortar. One of the earliest recorded references appeared in the 1853 novel “The Adventures of Mr. Verdant Green, an Oxford Freshman.”

Modern students have found a way to personalize the uniform dress: They decorate the tops of their caps. Messages range from the whimsical to the profound — pictures of pets to political statements.

Sheila Bock, an associate professor at University of Nevada Las Vegas and a folklorist, has been studying the practice since 2015. The oldest example she has found is a photo from the Vietnam War era, in which a graduation cap is decorated with peace sign as a form of protest. The practice has only evolved since then.

“When you really think about commencement, it’s a all about this show of community. This fact that everyone is dressed the same, and everyone is grouped,” she said by phone Tuesday. “Just by the very act of decorating the cap and personalizing it, you are kind of intervening in that institutional display.”

Bock has seen many graduation caps that make a statement about individuals’ identities. She recalls a cap from a recent graduate who was an undocumented immigrant — it had a quote written in Spanish about not forgetting where she comes from.

Bock also interviewed a gay man who graduated in the 1990s; he decorated his cap with bright flowers at a time when the LGBTQ community faced discrimination.

“It’s never explicitly stated that this group of people doesn’t belong,” Bock said. “But if you even think of the origins of the cap and gown, it has this European origin. The cap, for example, doesn’t fit on certain types of hair. It’s the implicit ways in which belonging is shown.”

While the caps often make broad statements, Bock was surprised in her work to find that many graduates do not decorate their attire to make a statement, they do it for personal reasons.

“They describe it as ‘I wanted to put my own touch on the ceremony,’” Bock said. “They want it to be an act of self-expression that people often use to share political ideas and ideals.”