Colin Dickey writes about cities and the dead for Lapham’s Quarterly.  From “Necropolis”:

Throughout early Christendom, bishops consolidated power around the tomb. The cemetery where St. Peter was buried was well outside of Rome’s city walls in a distant plot of land named Vatican Hill. But it was here, not in the city itself, that his followers built his basilica. The religious power base—in Tébessa, Nola, Rome, and elsewhere—had shifted to the periphery, creating an imbalance that could not last. One way or another, the saint would have to come inside the city.

In the French city of Arras, the bishop Vaast asked to be buried outside of the city per the Roman tradition. But upon his death in 540, his body miraculously became so heavy it could not be lifted; when the archpriest asked the corpse if it would rather be carried to the cathedral’s altar, it suddenly became light as a feather. Alternately, if you could not bring the saint to the city, you brought the city to the saint: Pope Leo IV began an expansion of Rome’s walls around 847 to include old St. Peter’s Basilica, and what had once been a peripheral cemetery was now the heart of the Holy Roman Empire.