The simple black judicial robe has been a part of my life for nearly four decades. I first wore one in 1975 when I became a trial judge in Arizona. When I was appointed to the Supreme Court of the United States, in 1981, I brought that same robe with me to Washington and wore it on my first day on the bench. Although I retired in 2006, I still wear a robe in my role as a “circuit-rider,” sitting frequently, as many retired justices do, on various federal Courts of Appeals across the country.

It is surprising to me how little we know about where this plain black judicial uniform comes from. Colonial judges in England wore robes, and the tradition took off on American soil as well. But English judges also wore colorful robes and ornate wigs—a tradition that was not adopted in the United States. Some speculate that the Supreme Court began with more colorful attire; the court’s official portrait of the first chief justice, John Jay, shows him in a robe of black and red with white borders. The story, perhaps apocryphal, is that Thomas Jefferson himself objected to such unnecessary pomp: As an ardent supporter of modest republican citizenship, Jefferson was against “any needless official apparel,” especially “the monstrous wig which makes the English judges look like rats peeping through bunches of oakum.” It is believed that by 1801, when John Marshall became chief justice, the justices were in the habit of wearing black.

Today, every federal and state judge in the country wears a very similar, simple black robe. I am fond of the symbolism of this tradition. It shows that all of us judges are engaged in upholding the Constitution and the rule of law. We have a common responsibility.

Remarkably, this similarity among our judges and justices is purely a matter of tradition. There are no rules that dictate what judges or justices must wear on the bench, nor is there even a common source for Supreme Court robes. The court’s internal correspondence suggests that, in the 19th century, the justices all wore black silk robes from a single tailor. By the 20th century, other materials were often used and judges selected their robes from those available to college graduates and choir singers. For the most part, we have all chosen to wear a very similar style of black judicial robe.

Of course, there have been a few exceptions, intentional or otherwise. In the marshal’s office records of the court, there is a note that in 1969, Justice Hugo Black “returned to the Bench” without his robe on and sat on the bench for the remainder of the court session, departing with his colleagues. But there’s no record of whether something happened to his robe or he just forgot to put it on. And Chief Justice William Rehnquist added gold stripes to one arm of his robe. It was an unannounced departure: He simply surprised us with the change one morning. He said he had recently seen a Gilbert & Sullivan opera in which the lord chief justice wore a robe with gold stripes. Our chief asked the seamstress at the court to sew some on his own robe. I myself made a modest addition to the simple black robe by choosing to wear a white judicial collar.

My fondest thoughts about my robe have to do with the tradition at the Supreme Court for putting it on. On argument days, a buzzer sounds about five minutes before the oral argument starts. The justices go to the robing room—the court’s version of a locker room. Each justice has a locker; attendants help the justices fasten their robes. Then the justices, without fail, engage in a wonderful custom. Each justice shakes the hand of every other justice before walking into the courtroom—an important reminder that, despite the justices’ occasional differences in opinion, the court is a place of collegiality and common purpose.

“People often ask me if, as the first woman on the Supreme Court, I had any special preferences for my robe.” says Sandra Day O’Connor. “But honestly, I took whatever was available and put it on.”