The practice of asylum (like the word itself) can be traced to ancient Greece, where particular altars and similar holy places offered sanctuary to fugitives, especially ill-used slaves. In the early Roman Republic the comparable custom protected aliens fleeing from other states, and though the practice was weakened during the first centuries of the Roman Empire, losing what little legality it originally possessed, the tradition that fugitives might seek at least temporary protection against those with greater physical power or apparent right reemerged with the establishment of Christianity. Churches were now designated as places of sanctuary, and the rights and duties of both fugitive and pursuer became formulated in increasing detail through imperial promulgations (such as the fifth-century Codex Theodosianus, books 9 and 16) and customary law. So it was for a thousand years in Europe until the Reformation began eroding such religious privileges—a process of abatement that continued until the late eighteenth century and the advent of the American and French revolutions.
As the authority of Rome and the Catholic Church declined, so conversely grew the power of the secular though usually Protestant state. For many centuries asylum had been understood as the granting of a privileged and protected area within a wider jurisdiction (the precincts of a church within the territory of a feudal lord). Since the seventeenth century, however, asylum has been understood as the creation by one jurisdiction (a "sovereign" state) of a privileged status for an individual from the reach of an opposing claimant, invariably another sovereign state whose "subject" the fugitive was. Thus, the common theme that links present-day notions and practices of asylum to those of the classical and premodern world is the special or "privileged" status of the would-be asylum-seeker vis-à-vis the state of original jurisdiction and the sought-after haven or sanctuary within a state of refuge.
Against this element of continuity, which emphasizes the individual's pursuit of safety from the executive and judicial power of one authority, has to be set the distinctive feature of asylum as it developed in the twentieth century, especially in the years since World War II. Now when the term "asylum" is used, attention focuses upon the mass movement of people. The involuntary migration of people, of minorities expelled or fleeing from a hostile majority, is nothing new: so it was for the Jews and Muslims after the Reconquista in Spain in the late fifteenth century and for the Huguenots in France following the revocation of the Edict of Nantes in 1685. In the twentieth century similar enforced population movements met the barriers created by the immigration policies of host countries. Thus, in the discourse of the early twentieth-first century, asylum became a term connoting mass migration, the laws and practices of host states in dealing with would-be immigrants, and the formal responsibilities of such states in the face of the legal rights and humanitarian demands of such alien refugees. The putative rights of a single individual are now overshadowed by the vision of those self-same rights exercised by thousands, even millions, of prospective incomers.
Given that the United States was rhetorically created partly as a haven for the oppressed; given the historical fact that the United States is a country of immigration ("a nation of nations"); and given the range of responsibilities that positive and customary international law now places upon the United States and all other sovereign states toward refugees, the issue of asylum has unsurprisingly become intensely debated and highly controversial. Even so, one element may be briefly—and relatively uncontentiously—explicated. Paradoxically, it is the topic that was once regarded as synonymous with asylum tout cour, namely diplomatic asylum.