As showing that the term “threshold” is not applied to these boundary stones merely by accommodation, it is sufficient to quote from Justinian in the case. He declares specifically that “as the threshold makes a certain boundary in a house, so also the ancients designed that the boundary of the empire should be its threshold; hence it is called the ‘threshold,’ as if it were a certain bound and term.”[502] Speaking of one who has been in foreign captivity, and who desires a resumption, or a restoration, of his civil rights, on his coming back to his country, Justinian says that such a return “is called _postliminium_ [a recrossing of the threshold], because at that same threshold the thing which he has lost is restored to him.”[503] When the old Portuguese navigators started out on their voyages of discovery, they were accustomed to take with them stone pillars to set up in a prominent place at the farthest limits of their newly claimed territory as the national door-posts or threshold in that direction. Such a pillar was erected at the mouth of the Congo River, at the time of its discovery by Diego Cão, or Cam, in 1484–85. On this account, the river was known for a time as the “Rio de Padrão,” or “Pillar River.”[504] It might, indeed, have been called the “River of the Threshold.” This custom of setting up stone pillars as boundary marks along the borders of countries, nations, and states, has been continued down to the present day. Such landmarks are still to be seen along the borders of the great divisions of Europe, and they are on the lines of the several states of the United States of America. The line between the English grants in America, originally made to the Duke of York and to Lord Baltimore, was, after much dispute, run by two English surveyors, Charles Mason and Jeremiah Dixon, in 1763–67, and marked by stone pillars at intervals of five miles. This was generally known as “Mason and Dixon’s line;” it separated Pennsylvania from Delaware, Maryland, and Virginia, and was the dividing line between the free and the slave states before the Civil War of 1861–65. One of those early stone landmarks on that line is still to be seen near Oxford, in Chester County, Pennsylvania, as an illustration of a practice beginning in Babylonia as far back as 4000 B.C., and continued in America down to A.D. 1895.[505] European titles of rank bear traces of the importance formerly attached to national boundary lines and their preservation. The old German title of “markgraf,” the “graf” or count or warden of the marches, designated a representative or servant of the king who was in charge of the “marches,” or “marks,” or “border lines,” which guarded the thresholds of the empire in different directions. It was under “Henry the Fowler,” early in the tenth century, that this title, as a title, first gained prominence. Afterwards it became hereditary; “and hence have come the innumerable margraves, marquises, and such like of modern times.”[506]