Answer:
   
   Customs, although relatively static, do change over time. Consider the
   following changes in customs between now and the 2nd Century CE:
     * R' Shim'on ben Gamliel, in the 2nd Century CE, was frustrated with
       the competitiveness in funeral arrangements. People felt that they
       weren't doing enough for their loved one if they didn't do as
       much--or out-do--their neighbors, sometimes to the point of
       impoverishment. He was a descendent of Hillel, a nasi (prince; ie
       not merely the rabbinic leader of the day, but also lauded for
       being a descendant of David), and quite wealthy. He insisted in
       his will that they bury him in a simple white linen garment,
       figuring that everyone would follow. And such became custom.
     * Jews in the 2nd Century CE placed the body of the deceased in the
       ground by using caves rather than digging graves. Usually there
       would be shelves in the walls of the cave, like a subterranean
       mausaleum. However, burial space was running low. So, after a
       year, when the body was reduced to dry bones, they would take the
       bones out of their original location, and re-bury them in a
       smaller box. (Note that this is similar to the custom seen today
       in family crypts in locations where the water table is too high,
       such as New Orleans)

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