If I were to ask you how many guards were at Jesus' tomb after he was placed there after he was crucified, you would instinctively say 'Two.' When I was teaching New Testament that was in fact the common answer. And who can blame anyone? Look at the art and presentation of the Easter story. Now, the text definitely makes it clear that there were more than two guards. This is clear enough from a reading of Matthew 28 which says that 'some of the guards went into the city and reported to the chief priests [what] had happened.' Clearly, 'some' of the guards means that others remained while others- not "one of the guards'" but "some of the guards" went into the city. For this to work it seems to me you'd need at least four guards. If these are in fact Roman guards, then four is in fact the minimum that protocol would dictate, with each man taking three hours out of the night. If pressed, I personally suspect that thirty to fifty guards were present but even if there were only sixteen it is virtually impossible that they all fell asleep and they all failed to notice a bunch of disciples slinking about, clawing at a honking big tombstone, and then extracting the body. We are talking about Roman soldiers here, after all.