Tomb of Peter

Given Christianity's central mystery–from death comes life—it is not surprising that bones of important people were incorporated into altars.  Or that entire churches were erected on the spot of a martyr's death.

One of the most important instances of this is Saint Peter's Basilica. Approximately twenty feet beneath the main altar lies the tomb of Saint Peter—the rock (Gr. petra) upon which Jesus said his church would be founded.

Archaeologists in the mid-twentieth century discovered that Constantine had leveled half of the hill cemetery to position his basilica closer to Peter's remains.  Moving earth from its top to the base for support, some tombs even had to be sawed in two.  

According to tradition, when Constantine founded the church he re-interred Peter's bones inside a great bronze chest capped with a gold cross. The sixth-century biography of the first ninety popes, known as the Liber Pontificalis (Lat. "Book of the Popes"), states that this chest measured 5 x 5 x 5 Roman feet. Archaeologists have never recovered the tomb, but the idea shaped the Christian image of Peter's tomb for seventeen hundred years nevertheless. 

And the image? 

The rock of Christ was a cube.

As the symbolic center and foundation of the church, a cubic omphalos connotes a firm and stable center.  Christian faithful over centuries took pride in the fact that Peter, so esteemed in the eyes of Jesus, had a burial tomb worthy of his stature: a perfectly symmetrical bronze cube with a majestic gold cross perched proudly on top.

The strongest intuitive symbol is widely agreed to be the cube.  The only rock foundation of the basilica was Peter's tomb which tradition held was a cube.  These ideas merged together over time and a powerful foundational symbol arose.