The “Great Writ” or habeas corpus has been an essential civil liberty guaranteed since Magna Carta. In listing powers denied to Congress, the Constitution notes that “The privilege of the writ of habeas corpus shall not be suspended, unless when in cases of rebellion or invasion the public safety may require it.” In 1861, Abraham Lincoln invoked this power of Congress—which was not in session—to suspend habeas corpus in certain areas. The next year, as he believed the civil justice system was inadequate to deal with the rebellion, he expanded the suspension throughout the United States and established military tribunals to try citizens charged with disloyalty. In this lesson, students explore Lincoln’s suspension of habeas corpus and constitutional issues surrounding it.