1324 BC
It's around that year that Pharaoh Tutankhamun died (sources vary, some say 1324 BC). His tomb was found and opened in 1922 AD, so more than 3000 years later. We tend to call those who did it archeologists as opposed to grave robbers and I agree that there's a difference whether you do it destructively and in secrecy for some personal profit or whether it's well documented and the results made accessible to the public, but when you think about it ... In both cases the tomb that was supposed to stay shut forever is opened and its treasures and the corpse removed.