The Framers were substantially influenced by ancient history and classical political theory, as exemplified by their education, the availability of classical readings, and their inculcation in classical republican values. Roman republican models of American constitutionalism, including the theory of mixed government as applied to the Roman constitution, and the distribution of powers among the organs and institutions of the Roman republic, were also well-understood by the Framers. This Article examines the deployment of Executive power in the Roman republic and its limitation by the Roman law doctrine of provocatio and the plebian tribune's power of auxilium, providing substantial protection to a Roman citizen's individual liberties and privileges under the law. Provocatio and auxilium could, however, be suspended under the Roman constitution by a decree in the Roman senate for the executive magistrates to take all measures necessary to safeguard the Republic. The Framers appreciated Roman constitutional history, and applied its lessons in designing many features of Executive authority in the U.S. constitution, particularly in the development and interpretation of the Habeas Suspension Clause. Roman analogues of provocatio and auxilium are relevant to three contemporary debates about the meaning and scope of the Suspension Clause: (1) whether the president may unilaterally suspend the privilege of habeas corpus, without prior congressional authorization; (2) whether Congress's determination of the conditions for suspension are ever subject to judicial review; and (3) whether a suspension can ever be performed retroactively for those already held in detention. Understanding the classical foundations of the American constitution can thus have a significant impact on the principles and methodologies for divining original intent, as well as appreciating the Constitution's structural and rights-protecting aspects.