All 100 Senators voted on the immigration bill from their desks. That’s a rarer occurrence than you might think.

To mark the significance of the vote on a sweeping immigration bill Thursday, Senate Majority Leader Harry Reid (D-Nev.) made the atypical request that senators sit at their assigned desks and stand to cast their votes from there as the roll was called.

What's up with that?

There's actually a requirement on the books that senators vote from their desks, but it's rarely enforced. In 1984, Democratic Sen. Jennings Randolph of West Virginia introduced a resolution to require that senators vote from their assigned desks. It passed, formalizing a rule that, well, hasn't been formally followed all that much. During most votes, it's customary for the senators to enter the Senate well, cast their votes, and go about their business.

The majority leader has the power to require, as Reid did Thursday, that senators vote from their desks. Since 1984, 30 such votes have been taken, mostly on legislation seen as significant or historic, according to a tally from the Senate Historian's office.

Six of justices who currently sit on the Supreme Court were confirmed in such votes. Votes on the health-care reform law, a resolution to commend troops and intelligence efforts for the killing of Osama bin Laden, and articles of impeachment against Bill Clinton are other examples.

The method has also been deployed in cases where a lot of votes must be taken in succession. In fact, the most recent occasion when senators voted from their desks was during the so-called "vote-a-rama" in March.

You can check out the complete history of senators voting from their assigned desks dating back to 1978 here, courtesy of the Senate Historian's office.

— Ed O'Keefe contributed to this post