According to Dei'ah veDibur, old Troyes was destroyed by fire, and
(Via a comment on Yeranen Yaakov, which also has some fun Rashi facts)
the town had since undergone a transformation. All that the fire left of its wooden houses were ashes and charcoal. Ordinarily, it would have been impossible to ascertain where the ancient Jewish graveyard had been. The boundaries of the built-up area had also changed completely.
"But one day the professor came to me with a beaming face" [said Rav Yisroel Meir Gabbai]. From his expression it was easy to guess what he had discovered — an old map, hundreds of years old, that clearly showed the area of the old cemetery. According to the information in Seder Hadoros, Rashi is buried in that cemetery. Further investigations had to be made in order to locate the actual area. Scientific methods had to be employed in order to verify the evidence . . . We very soon discovered that we were standing on the area of the cemetery.
Rav Gabbai: "It was clearly providential that nobody had interfered with the site. The square in which the cemetery was located had remained unbuilt. Generations of Frenchmen had left it alone. Sadly, the nearby road encroached on a small part of the cemetery. Concrete belonging to two corner buildings had been poured over the area of the graves. But besides these exceptions everything remained open."
A year after the discovery, the Jews of France erected a monument at the site — an impressive black and white globe engraved with the letter shin. The accompanying sign said a few words about Rashi but gave no indication that the entire area was an ancient Jewish cemetery.
None of the locals or visitors realized that in walking across the square they were treading on holy ground, over the heads of a holy community that placed its imprint upon the soul of a nation.