I saw an encore showing last night. What a great special! For those who may have missed it, this article provides an overview:
Long story short: When the Emporer Costantine had the earth beneath the Pagan temple removed, the solid rock of Christ’s tomb remained, then covered by the original edicule to protect it. Over the years when the edicule needed restoration the original edicule was not removed, rather a new one built over it… and later another over it and so on, like nested Russian eggs. Four edicules, the latest build in 1810, now cover the tomb of Christ and the rock portions of the cave-like tomb may still be intact beneath all of them; just as the rock of Calvary is still today visable under glass panels in the nearby chapel.
When the 1810-built edicule needs restoration in the near future, it may be possible to uncover the previous three edicules and expose the actual rock of Christ’s tomb itself.