Mary Ziegler, the author of several books on the history of abortion (and a critic of the draft decision), said that part was correct.But the opinion, she and others argue, underplays the fact that for most of the first 100 years of American history, early abortions — before fetal “quickening” (generally defined as the moment when the fetus’s movements can be detected) — were not illegal.

This is the argument made in the historians’ brief, which outlines the history of abortion regulation up to 1866. For decades after the founding of the United States, common law did not regulate abortion, or even recognize that abortion was happening at that early stage. “That is because common law did not even acknowledge a fetus as existing separately from a pregnant woman” before quickening, the historians argue.

The central historical claims in Roe “were accurate,” the brief says, “and remain so today.”

Leslie J. Reagan, the author of “When Abortion Was a Crime: Women, Medicine and Law in the United States, 1867 to 1973,” said in an interview that abortion was common in the early 19th-century, perhaps even more so than Roe depicted.

And regulation relied on women’s own experience, since they were the ones who would know when “quickening” occurred. And before “quickening,” Professor Reagan said, taking medications or other treatments wasn’t even considered abortion, but “trying to get your menses” — menstrual period — “back.”

“It was after quickening that it was against the law, and considered immoral,” she said. “After quickening, women themselves would stop trying to get their menses back. It was considered a life.”

Justice Alito’s Sources

While the draft makes references to the historians’ brief, it relies more heavily on other sources, including “Dispelling the Myths of Abortion History,” a 2006 book by Joseph W. Dellapenna that challenged Justice Blackmun’s historical arguments in Roe.