what were these "tomb of David" or "tomb of David and Solomon" in post-exilic Israel?

from Wikipedia article on John Hyrcanus, ruled 134-104BC

from this http://www.livius.org/he-hg/herodians/herod_the_great02.html article on Herod the Great:

Yes, so what exactly were these “tombs” (or maybe just one tomb) filled with treasure available for looting? Since the time of David and Solomon Jerusalem got sacked and/or forced to pay big tribute couple of times. Then it got completely destroyed by the Babylonians, presumably along with massive looting. Then it got rebuilt by the returned exiles and subsequently suffered at least one enemy occupation, during the Maccabean revolt. After such long and eventful history, where could this tomb treasure come from? Was it a cult center that accumulated wealth from donations, like Temple on small scale? Or what do we know about it?