These particular tombs were inaccessible, but we were able to enter some of the spectacular tombs in the Lycian city of Tloss. (Patricia, who grew up on Roger Corman films, was particularly thrilled.) Each tomb had niches for exactly three bodies.
Why three? Why these tombs at all? History does not tell us: the structures themselves, long looted, are the only evidence.
By the way, if you've never heard of Lycia and Caria, don't feel embarrassed. Nothing really ever happened there--- no history at all in its conventional sense, meaning conquests, battles, famous leaders, etc. The area was (and remains) rich, protected by the natural walls of the Tauros mountains to the north, and by the Mediterranean to the south. The people there were wealthy in their isolation, concentrated on making money and living the good life, and then leaving a beautifully-housed corpse.
I expect this area will inspire a number of stories from me. If only I can find time to write them.